Etymology: Etymology tree Proto-Germanic *fastuz Proto-West Germanic *fast Old English fæst Middle English fast English fast From Middle English fast, fest, from Old English fæst (“firm, secure”), from Proto-West Germanic *fast, from Proto-Germanic *fastuz; see it for cognates and further etymology. The development of “rapid” from an original sense of “secure” apparently happened first in the adverb and then transferred to the adjective; compare hard in expressions like “to run hard”. The original sense of “secure, firm” is now slightly archaic, but retained in the related fasten (“make secure”). Also compare close meaning change from Latin rapiō (“to snatch”) to Latin rapidus (“rapid, quick”), from Irish sciob (“to snatch”) to Irish sciobtha (“quick”).

Firmly or securely fixed in place; stable.
“That rope is dangerously loose. Make it fast!”
Firm against attack; fortified by nature or art; impregnable; strong.
“out-lawes […] lurking in woods and fast places”
Steadfast, with unwavering feeling. (Now mostly in set phrases like fast friend(s).)
“I still hear you sayin', "Dear one, hold me fast"”
Moving with great speed, or capable of doing so; swift, rapid; light.
“I am going to buy a fast car.”
Moving with great speed, or capable of doing so; swift, rapid; light.
“Plutonium-240 has a much higher fission cross-section for fast neutrons than for thermal neutrons.”
Of a place, characterised by business, hustle and bustle, etc.
“Sydney is a fast city, and the pace is becoming increasingly more frantic.”
Causing unusual rapidity of play or action.
“a fast racket, or tennis court”
“a fast track”
Able to transfer data in a short period of time.
“But at the microlevel it consists of an unimaginable number of atoms connected by springy chemical bonds, all jiggling around at a rate that even our fastest supercomputer might envy.”
Deep or sound (of sleep); fast asleep (of people).
“Since his majesty went into the field, I have seen her rise from her bed, throw her nightgown upon her, unlock her closet, take forth paper, fold it, write upon’t, read it, afterwards seal it, and again return to bed; yet all this while in a most fast sleep.”
Not running or fading when subjected to detrimental conditions such as wetness or intense light; permanent.
“All the washing has come out pink. That red tee-shirt was not fast.”
“Mineral pigments were probably the first materials used for dyeing. They were generally not fast to water.”
Tenacious; retentive.
“Roses, damask and red, are fast flowers of their smells.”
Having an extravagant lifestyle or immoral habits.
“a fast woman”
“[…] we remember once hearing a fast man suggest that they were evidently "nobs who had overdrawn the badger by driving fast cattle, and going it high" — the exact signification of which words we did not understand […]”
Uncharacteristically mature or promiscuous for one's age.
“[…] if she is of the slightly faster kind that gives smart lunch parties at the Strand Corner House, her diet is sometimes a little stronger; she takes to novels of the orchid house and the tiger's lair, to the artless erotics of Miss Elinor Glyn, Mr Hubert Wales, and Miss Victoria Cross.”
Ahead of the correct time or schedule.
“There must be something wrong with the hall clock. It is always fast.”
More sensitive to light than average.

adv

Etymology: From Middle English fast, faste, from Old English fæste, from fæst + -e (adverb-forming suffix).

In a firm or secure manner, securely; in such a way as not to be moved; safe, sound .
“Hold this rope as fast as you can.”
“Do as I bid you, ſhut doores after you, Faſt binde, faſt finde, A Prouerbe neuer ſtale in thrifty minde.”
Deeply or soundly .
“The princess was sleeping fast, and her servants were fast asleep too.”
Immediately following in place or time; close, very near .
“The horsemen came fast on our heels.”
“Fast by the sturdy batsman the ball unheeded sped. / That ain't my style, said Casey. Strike one, the umpire said.”
Quickly, with great speed; within a short time .
“Do it as fast as you can.”
“Faster than a speeding bit, the internet upended media and entertainment companies. Piracy soared, and sales of albums and films slid. Newspapers lost advertising and readers to websites. Stores selling books, CDs and DVDs went bust. Doomsayers predicted that consumers and advertisers would abandon pay-television en masse in favour of online alternatives.”
Ahead of the correct time or schedule.
“I think my watch is running fast.”

intj

Ellipsis of stand fast, a warning not to pass between the arrow and the target.

name

Etymology: Abbreviation. Coined in recognition of the word fast, e.g. (medical sense) describing the need for speedy diagnosis and treatment.

Initialism of Five-hundred-meter Aperture Spherical Telescope.

noun

Etymology: From Middle English faste, fasten, from Old English fæsten (“fast, fasting”), from Proto-West Germanic *fastuni, from Proto-Germanic *fastu(b)nją (“fast, fasting”). Cognate with Old Frisian festene, feste (Modern West Frisian fêsten, fêste), Middle Dutch vastene (Modern Dutch vasten), Middle Low German vastene (Modern German Low German Fasten), German Faste, Fasten (“fast, fasting”), Gothic 𐍆𐌰𐍃𐍄𐌿𐌱𐌽𐌹 (fastubni, “fasting”). Possibly merged with Old Norse fasta (“fast, fasting”), whence also Danish faste (“fast, fasting”), Swedish fasta (“fast, fasting”).

The act or practice of fasting, religious abstinence from food.
“1677 George Fox, The Hypocrites Fast and Feast Not God's Holy Day, p. 8 (paraphrasing Matthew 6:16-18). And is it not the Command of Christ, that in their Fast they should not appear unto men to fast?”
“anciently a change of diet was not reckoned a fast; but it consisted in a perfect abstinence from all sustenance for the whole day till evening.”
Any of the fasting periods in the liturgical year.
“1662 Peter Gunning, The Holy Fast of Lent Defended Against All Its Prophaners: Or, a Discourse, Shewing that Lent-Fast was First Taught the World by the Apostles (1677 [1662]), p. 13 (translation of the Paschal Epistle of Theophilus of Alexandria). And so may we enter the Fasts at hand, beginning Lent the 30th. day of the Month Mechir”

phrase

Etymology: Abbreviation. Coined in recognition of the word fast, e.g. (medical sense) describing the need for speedy diagnosis and treatment.

Acronym of facial drooping, arm weakness, speech difficulty, time, a mnemonic for diagnosing a CVA or stroke.

verb

Etymology: From Middle English fasten, from Old English fæstan (“to fast”), from Proto-West Germanic *fastēn, from Proto-Germanic *fastāną (“to fast”), from the same root as Proto-Germanic *fastijaną (“to fasten”), derived from *fastuz, and thereby related to Etymology 1. The religious sense is presumably introduced in the Gothic church, from Gothic 𐍆𐌰𐍃𐍄𐌰𐌽 (fastan, “hold fast (viz. to the rule of abstinence)”). This semantic development is unique to Gothic, the term glosses Greek νηστεύω (nēsteúō), Latin ieiuno which do not have similar connotations of "holding fast". The feminine noun Old High German fasta likely existed in the 8th century (shift to neuter Old High German fasten from the 9th century, whence modern German Fasten). The Old English noun originally had the sense "fortress, enclosure" and takes the religious sense only in late Old English, perhaps influenced by Old Norse fasta. The use for reduced nutrition intake for medical reasons or for weight reduction develops by the mid-1970s, back-formed from the use of the verbal noun fasting in this sense (1960s).

To practice religious abstinence, especially from food.
“Thou didst fast and weep for the child.”
“Fasting he went to sleep, and fasting waked.”
To reduce or limit one's nutrition intake for medical or health reasons, to diet.
“The ideal would be to fast in a situation where you are not tempted by food”
“After the equilibration period, the rats designated for deprivation studies were made to fast for 24, 48, 72, or 96 hr according to experimental design.”
To cause (a person or animal) to abstain, especially from eating.
“At 11 weeks of age, all mice were fasted overnight and underwent gallbladder ultrasonography to determine ejection fraction.”
“Kittens, when fasted overnight, were not hypoglycemic (<60 mg/dl).”