Old English fæst "firmly fixed, steadfast, constant; secure; enclosed, watertight; strong, fortified," probably from Proto-Germanic *fastu- "firm, fast" (source also of Old Frisian fest, Old Norse fastr, Dutch vast, German fest), from PIE root *past- "firm, solid" (source of Sanskrit pastyam "dwelling place").
Meaning "rapid, quick" is from 1550s, from fast (adv.) , in which entry the attempt is made to explain how a root meaning "firm, solid" came variously to yield words for "refrain from eating" (fast (v.)) and "rapid, quick." Of colors, from 1650s; of clocks, from 1840. The sense of "living an unrestrained life, eager in pursuit of pleasure" (usually of women) is from 1746 (fast living is from 1745).
Fast buck recorded from 1947; fast food is first attested 1951. Fast lane is by 1966; the fast track originally was in horse-racing (1934), one that permits maximum speed; figurative sense by 1960s. Fast-forward is by 1948, originally of audio tape.
"abstain from food," Old English fæstan "to fast" (as a religious duty), also "to make firm; establish, confirm, pledge," from Proto-Germanic *fastanan "to hold, guard," extended to the religious act "observe abstinence" (source also of Old Frisian festia, Old High German fasten, German fasten, Old Norse fasta "abstain from food"), from the same root as fast (adj.).
The original meaning in prehistoric Germanic was "hold firmly," and the sense evolved via "have firm control of oneself," to "hold oneself to observance" (compare Gothic fastan "to keep, observe," also "to fast"). Perhaps the Germanic sense shifted through use of the native words to translate Medieval Latin observare in its sense "to fast," or it might have been a loan-translation of a Greek expression brought to the Goths by Arian missionaries and spread from them to other Germanic peoples. The verb in the sense "to make fast" continued in Middle English, but was superseded by fasten. Related: Fasted; fasting.
Old English fæste "firmly, securely; strictly;" also, perhaps, "speedily," from Proto-Germanic *fasto (source also of Old Saxon fasto, Old Frisian feste, Dutch vast, Old High German fasto, German fast "almost," but in earlier use "firmly, immovably, strongly, very"), from *fastu- (adj.) "firm, fast" (see fast (adj.)).
The meaning "quickly, swiftly, rapidly" was perhaps in Old English, certainly by c. 1200, probably from or developed under influence of Old Norse fast "firmly, fast." This sense developed, apparently in Scandinavian, from that of "firmly, strongly, vigorously" (to run hard means the same as to run fast; also compare fast asleep, also compare Old Norse drekka fast "to drink hard," telja fast "to give (someone) a severe lesson"). Or perhaps from the notion of a runner who "sticks" close to whatever he is chasing (compare Old Danish fast "much, swiftly, at once, near to, almost," and sense evolution of German fix "fast, fixed; fast, quick, nimble," from Latin fixus). The expression fast by "near, close, beside" also is said to be from Scandinavian. To fast talk someone (v.) is recorded by 1946.