Beyond German, a prominent example of consonant shift is that almost everybody else's /S/ somehow often became an /H/ sound in Greek, particularly at the beginning of a word. In Greek spelling itself, one sees a back-accent on the initial vowel, since Greek did not have a letter for the breathy modern /H/ sound. For example, Greek òμος would be transliterated as homos. As discussed below, this corresponds to "same" and "similar". You have to look very carefully, though, because all Greek words that start with a vowel have the vowel accented — a grave or "back" accent means "breathy" while an acute or "forward" accent means it is pronounced with the normal vowel sound. For example, /ò/ is pronounced "ho" but /ó/ is pronounced "oh", so the Greek spelling of Homer is Òμηρος, but octopus is óκτωπους.
I had to qualify that "almost everybody else" comment because Old Persian and Armenian also have the same /H/ for /S/ switch. There are enough other similarities between Old Persian and Greek to convince the scholars that they were once essentially the same language before the Greeks moved westward. Since they are two of the most archaic living ie languages, along with Lithuanian, it's been said that one can achieve "Instant Proto-Indo-European" by combining Sanskrit consonants with Greek vowels. [20Nov07] (Sanskrit very faithfully preserved the Indo-European consonant structure, including some "breathy" ones like /BH/ and /DH/ now uncommon elsewhere, but then messed things up by rather abruptly eliminating the vowels /E/ and /O/ — both were changed into /A/. For example, Greek dedorka means "I saw", while the Sanskrit equivalent is dadarsa, Latin rex is Sanskrit raj-, etc.)
Welsh also uses an /H/ for ie /S/ in some cases. See below for a couple of examples.
Here are some obvious parallels: An Indo-European sem- root meaning "one" led to Germanic same, Latin sim- (simultaneous, similar, simulate, resemble, ensemble, single, simple, facsimile, and many others), but Greek homo- as in homogenize, homosexual, homonym (same name), etc. [22Feb06] Anomaly is from an-homos, not the same, an irregularity. Latin semper, always, is sim-per, the same throughout; the word is familiar from mottos like Semper Fidelis of the "always faithful" US Marines, and Semper Paratus of the "always prepared" Boy Scouts and Coast Guard.
Exactly the same sequence is in Germanic some, Latin semi-, but Greek hemi-, both the latter now meaning "half." Ditto Germanic salt, Latin sal- (saline, salary, and the whole salad, salsa, sauce, sausage, salami, slaw, sassy, souse family), but Greek hal- (halide, halogen). In numerals, we have Germanic six and seven, Latin sex- and sept-, but Greek hex- and hept-.
Latin solid is Greek holo- (entire) as in hologram (entire picture) and catholic (kath-holikos, concerning the whole, i.e., universal). Holocaust means entirely burned — the word originally meant a sacrificial animal which was really and truly burned, as opposed to symbolically burned and then eaten. The last element is also in caustic, cauterize, and the very non-obvious ink, violently shortened from Greek enkauston, "burned in". Roman central heating was provided by a so-called hypocaust, a furnace "burning under" the floor. That nicely segues to the connection between Latin sub and super- (under and over, respectively) and Greek hypo- and hyper-.
Germanic sun is Latin sol and Greek hel- — helium is so-named because it was detected in the spectrum of the sun before it was ever found on earth. Incidentally, Welsh for "sun" is haul.
The opposite of homosexual is heterosexual, and that is yet another example of the same process. Greek hetero- means "other", and it is from the same root as Latin compounds in se- and sed-, with the meanings of "other", "apart", or "without". Examples are seduce (to lead away), secret (divided off), sever (modern French sevrer means to wean), secure (without care, Latin cara), seclusion (closed away), etc. etc. Second means "other" or "following", whether it is the second item in a list or the second at a duel. Sedition is "going away", from Latin iter, journey. To separate is literally to set something aside for the future; in Latin parere meant to make ready, as also in prepare, to make ready beforehand, and repair, to make ready again. Several is simply a variant of "separate."
Pursuing this sequence, segue is the French form. Latin socius meant "follower" but came to mean "companion", leading to social, society, associate, its opposite dissociate, and soccer (short for "association football". I suppose it should be pronounced "sosher" or "sosser", but the spelling won out, just as it did in another British clipping, namely zoo. That's clipped down from "zoological garden", with both /O/'s at the beginning pronounced, so a zoo should theoretically be pronounced ZOH-uh). (Other relatives of zoo are the two-syllable name Zoe ("life") and the zodiac, shortened from Greek kuklos zodiakos, circle of animals.)
Both a sign and a signal are something to be followed, with the sense developing to "distinguishing mark", as in signing one's name. Something insignificant does not have such a mark. An ensign is a flag or standard to be followed into battle; as a military rank it is short for "ensign-bearer" — one who carries the insignia. To resign something was to remove the [owner's] mark or seal and assign or consign it to another, which makes it the opposite of re-sign.
Still more "following" or "with" words are sue, ensue, pursue, consecutive, sequel, consequence, persecute, set, suit, suite, and so on. Executor and executioner were once used indifferently — executors could chop off heads and executioners could probate wills. Either way, it is ex-sequi, to "follow out" or as we would now say, "carry out" an assigned task. C.f. the computer which executes a program, the business executive, etc. The current meaning of "carry out capital punishment" once had to be qualified: to "execute to death", translating French exécuter à mort. Today's readers probably jump at the once-common phrase, "God executes indifferent justice", where indifferent literally means "impartial", not "apathetic".
There are three closely related and often-confused terms used to describe the similarities between certain words: homograph, homophone, and homonym.
[25May08] By the way, the two meanings of base — a support and low or inferior — are not related. The former is from Greek basis, a step or foundation, while the latter is Latin bassus, short and fat. A bass singing voice is below the others; it doesn't support them. Since a basis is normally below other parts of something, the two words have been confused for a long time. Abyss and abysmal look like they might somehow be related to one or the other, but they are Greek a-byssos, no bottom, from bathos, depth. Abysmal didn't acquire its current meaning of "very bad" until the 20th century, before that it only meant "bottomless", as in "the abysmal ocean". Bathos itself is responsible for bathetic and the bathyscape and bathysphere used for deep-sea exploration, while geologists call a large intrusive mass of igneous rock a batholith.
Sometimes the meanings of a single word have diverged widely enough that the results are regarded as separate words: the homonyms bow (to bend at the waist) and the bow of a ship are ultimately from the same "bend" root, as are bow and arrow and bow tie. The latter pair are homographs of the first pair, of course, as well as homophones of the unrelated beau. For that matter, the first pair also have a homophone, bough! Similarly, all the meanings of bank are ultimately the same word. Deed, an action, is ultimately the same as deed, a legal document.
P.S. — Anyone who dislikes this aspect of English is strongly advised not to move to China. The Chinese rule that words be of one syllable means that there may be fifteen or twenty homophones of almost every word, although in the written language each might be represented by a different character. This is the main reason Chinese can't easily switch to a phonetic writing system, and it is the reason that Chinese poetry, where the poet tries to create multiple levels of meaning and ambiguity, is utterly untranslatable except at the most crude level.
Digressing slightly, the sem- root that means "same" is also in Russian samovar and samizdat (self-boiler and self-publishing, respectively) and the samoyed breed of dog, originally the Russian name for a certain Siberian tribe. The last syllable is the root in "eat" and "edible", so they were thought to be "self-eaters", i.e., cannibals. "Samizdat" is a triple compound of sam- -ex- (out), and -dat (give), i.e., "given out by oneself". The "same" root is also in the language called Sanskrit, where it means "together".
The "sleep" root that gave Latin soporific and insomnia (not sleeping) produced Greek hypnotic. [26May08] An Indo-European swad- root meaning "pleasant" produced English sweet, Latin suave and persuade, but Greek hedonism.
The root behind all the Latin and German sit family led to (sit, set, seat, session, sedate, settle, saddle, etc.) [26May08] Preside meant both "sit in front" [of an assembly] and also "guard" — a Spanish presidio in the American Southwest is a fort. Meanwhile, "sit" became hed- in Greek. Since kat- means "downward" in Greek (catastrophe, cataclysm, cataract, etc.), "sit down" was kat-hedra, which became their word for chair or throne. English cathedral is a direct descendant, since a "cathedral church" is literally a "throne church" — i.e., it features the throne (cathedra) of a bishop. Chair is the same Greek word after the French mangled it, as is chaise. Note that a bishop's see also means seat. The biblical council called the Sanhedrin is Greek for "sit together".
The -set in English place names (Summerset, and so on) means "seat" again, as in one's "country seat." An obsession is another "sit" relative — it literally means to "sit before" and was originally a military word now replaced by yet another "sit" relative — a siege. Siege also once meant throne — c.f. the Siege Perilous, the empty seat at King Arthur's round table reserved for the finder of the Grail. Alsatians "sit on the other side" [of the Rhine]. To reside is to "sit back". or rest. This came to mean "remain behind", leading to residue and residual. Sediment, meanwhile, is that which settles. It's a real stretch, but nest has the same translation as cathedral and chair. The root is ni-sed, to sit down. [17Sep07] One word sorely missed in English is the German Sitzfleisch, defined as the ability to endure something for a long period of time. It is literally "sitting-flesh", implying the possession of a hard or numb posterior.
[17Sep07] Somewhat improbably, size is derived from "sit"! Latin ad-sedere was used to mean consult with, literally to "sit beside" a judge or other official. French turned this into assize and assess, to judge. As a noun, "assize" came to mean "fixed quantity", and "size" evidently came from that being perceived as "a size"! Note that an assets is not related to "assess". (Yes, that is correct English — "assets" is singular.)
[26Feb08] Even more improbably, Sudafed® is derived from "sit"! The drug's real name is pseudoephedrine, an alkaloid which mimics the action of adrenaline. Ephedra is the plant genus from which the chemical ephedrine was first extracted. [10May08] Note that pseudoephedrine is now a "pseudo-controlled" drug, kept behind the counter and for which the customer has to sign. This is because it is fairly simple to convert it into methamphetamine, i.e., "speed". Federal drug officials finally began to get suspicious of people buying a ton of cold medicine at a time.
Other kata- "down" words in addition to the ones already mentioned are those from Latin cadere, to fall. They include the occident and accident family, q.v.
The Latin servare in words like conserve, preserve, reserve, and reservoir means "protect" or "guard", and that's what a Greek hero (protector) is known for. The Greek goddess Hera is the feminine form, and Hercules (Greek Herakles) is "glory of Hera". His name is quite sarcastic, since he was the son of Zeus and a mortal woman named Alcmene, and Hera, Zeus's wife, did not think kindly of the child, to put it mildly. She tried to kill him at least twice.
Observe doesn't quite look like it belongs to the "hero" tribe, but it is a short jump from "guard" to "watch carefully". This is particularly obvious in terms like an "observant Jew", meaning one who scrupulously adheres to the precepts of Judaism. (There's an unrelated Latin verb servire which meant serve, also seen in service, servant, and deserve, which originally meant to serve well.)
An ie su- root meant pig, leading not only to sow and swine, but Greek hyena, regarded as a notably repulsive animal. (Syphilis was the title of an early poem about that disease, and seems to mean "pig-lover", from su- and -phile.) Sticking to diseases, Latin serp- as in serpent is Greek herpes, to creep, from the progress of the lesions. Herpetology is the scientific study of snakes. (Another skin problem named for its "creeping" from place to place is ringworm, for which the Latin medical term is serpigo. Otherwise the two are unrelated — herpes is a virus infection while ringworm is a fungus.)