fast

UK: /ˈfɑːst/ US: /fæst/ ,(fast, fäst)

Inflections of 'fast' (adv):

faster

adv comparative

fastest

adv superlative

Inflections of 'fast' (adj):

faster

adj comparative

fastest

adj superlative

WordReference Random House Learner's Dictionary of American English © 2025

fast¹ /fæst/   adj. andadv., -er, -est. 
adj. 

1. moving or able to move, operate, function, or take effect quickly;
   quick;
   swift;
   rapid:
   a fast horse.
2. done in or taking comparatively little time:
   a fast race.
3. Time (of a timepiece) indicating a time in advance of the correct time:
   My watch is fast.
4. characterized by unrestrained or immoral conduct, esp. in sexual relations;
   wanton;
   loose:
   a fast crowd.
5. characterized by extreme energy and activity, esp. in the pursuit of pleasure:
   leading a fast life.
6. permanent, lasting, or unchangeable:
   a fast color.
7. resistant (often used in combination):
   acid-fast; Her clothes are color-fast (=won't lose color when washed).
8. firm;
   loyal;
   devoted:
   fast friends.
9. Informal Terms
   • (of money, profits, etc.) made quickly or easily and sometimes deviously:
     They made a few fast profits.
   • cleverly quick and manipulative in making money:
     a fast operator.

adv. 

10. quickly, swiftly, or rapidly:
    She drove very fast.
11. tightly;
    firmly:
    held on fast to my hand; caught fast in a trap.
12. in a fixed and secure way, as a door, gate, or shutter:
    The door was shut fast and locked.
13. soundly:
    He was fast asleep.
14. ahead of the correct or announced time:
    My alarm clock is running fast.

Idioms

15. Idioms pull a fast one, to engage in unexpectedly unfair or deceitful behavior to achieve one's goal:
    He pulled a fast one by sabotaging my computer files.

fast² /fæst/  v. [no object]

1. to eat no food.
2. to eat only a little or only certain kinds of food, esp. as a religious observance.

n. [countable]

3. an act or a period of not eating food, or a limiting of one's food.

WordReference Random House Unabridged Dictionary of American English © 2025

fast¹  (fast, fäst), adj., -er, -est, adv., -er, -est, n. 
adj. 

1. moving or able to move, operate, function, or take effect quickly;
   quick;
   swift;
   rapid:
   a fast horse;
   a fast pain reliever;
   a fast thinker.
2. done in comparatively little time;
   taking a comparatively short time:
   a fast race; fast work.
3. Time (of time)
   • indicating a time in advance of the correct time, as of a clock.
   • noting or according to daylight-saving time.
4. adapted to, allowing, productive of, or imparting rapid movement:
   a hull with fast lines; one of the fastest pitchers in baseball.
5. characterized by unrestrained conduct or lack of moral conventions, esp. in sexual relations;
   wanton;
   loose:
   Some young people in that era were considered fast, if not downright promiscuous.
6. characterized by hectic activity:
   leading a fast life.
7. resistant:
   acid-fast.
8. firmly fixed in place;
   not easily moved;
   securely attached.
9. held or caught firmly, so as to be unable to escape or be extricated:
   an animal fast in a trap.
10. firmly tied, as a knot.
11. closed and made secure, as a door, gate, or shutter.
12. such as to hold securely:
    to lay fast hold on a thing.
13. firm in adherence;
    loyal;
    devoted:
    fast friends.
14. permanent, lasting, or unchangeable:
    a fast color; a hard and fast rule.
15. Informal Terms
    • (of money, profits, etc.) made quickly or easily and sometimes deviously:
      He earned some fast change helping the woman with her luggage.
    • cleverly quick and manipulative in making money:
      a fast operator when it comes to closing a business deal.
16. [Photog.]
    • Photography (of a lens) able to transmit a relatively large amount of light in a relatively short time.
    • Photography (of a film) requiring a relatively short exposure time to attain a given density.
17. Sport [Horse Racing.]
    • (of a track condition) completely dry.
    • (of a track surface) very hard.
18. Informal Terms, Idioms pull a fast one, to play an unfair trick;
    practice deceit:
    He tried to pull a fast one on us by switching the cards.

adv. 

19. quickly, swiftly, or rapidly.
20. in quick succession:
    Events followed fast upon one another to the crisis.
21. tightly;
    firmly:
    to hold fast.
22. soundly:
    fast asleep.
23. in a wild or dissipated way.
24. ahead of the correct or announced time.
25. [Archaic.] close;
    near:
    fast by.
26. Idioms play fast and loose. See play (def. 76).

n. 

27. a fastening for a door, window, or the like.

• bef. 900; Middle English; Old English fæst firm; cognate with Dutch vast, Old Norse fastr firm, German fest; akin to fast²

Synonyms

• 1, 2. fleet, speedy. See quick. 
• 5. dissipated, dissolute, profligate, immoral; wild, prodigal.
• 8. secure, tight, immovable, firm.
• 9. inextricable.
• 13. faithful, steadfast.
• 14. enduring.
• 21. securely, fixedly, tenaciously.
• 23. recklessly, wildly, prodigally.

Antonyms

• 1, 2. slow.
• 5, 6. restrained.
• 8. loose.

fast²  (fast, fäst), v.i. 

1. to abstain from all food.
2. to eat only sparingly or of certain kinds of food, esp. as a religious observance.

v.t. 

3. to cause to abstain entirely from or limit food;
   put on a fast:
   to fast a patient for a day before surgery.

n. 

4. an abstinence from food, or a limiting of one's food, esp. when voluntary and as a religious observance;
   fasting.
5. a day or period of fasting.

• bef. 1000; Middle English fasten, Old English fæstan; cognate with German fasten, Gothic fastan, Old Norse fasta

fast³  (fast, fäst), n. 

1. Nautical, Naval Terms a chain or rope for mooring a vessel.

• Old Norse festr mooring rope
• alteration, by association with fast¹, of late Middle English fest, perh. noun, nominal use of fest, past participle of festen to fasten, or 1670–80

Collins Concise English Dictionary © HarperCollins Publishers::

fast / fɑːst/ adjective

1. acting or moving or capable of acting or moving quickly; swift
2. accomplished in or lasting a short time: fast work, a fast visit
3. (prenominal) adapted to or facilitating rapid movement: the fast lane of a motorway
4. (of a clock, etc) indicating a time in advance of the correct time
5. given to an active dissipated life
6. of or characteristic of such activity: a fast life
7. not easily moved; firmly fixed; secure
8. firmly fastened, secured, or shut
9. steadfast; constant (esp in the phrase fast friends)
10. (of a playing surface, running track, etc) conducive to rapid speed, as of a ball used on it or of competitors playing or racing on it
11. that will not fade or change colour readily: a fast dye
12. proof against fading
13. requiring a relatively short time of exposure to produce a given density: a fast film
14. permitting a short exposure time: a fast shutter
15. a deceptive or unscrupulous trick (esp in the phrase pull a fast one)
16. fast worker ⇒ a person who achieves results quickly, esp in seductions

adverb

1. quickly; rapidly
2. soundly; deeply: fast asleep
3. firmly; tightly
4. in quick succession
5. in advance of the correct time: my watch is running fast
6. in a reckless or dissipated way
7. fast by, fast beside ⇒ close or hard by; very near
8. play fast and loose ⇒ to behave in an insincere or unreliable manner

Etymology: Old English fæst strong, tight; related to Old High German festi firm, Old Norse fastr

fast / fɑːst/ verb

1. (intransitive) to abstain from eating all or certain foods or meals, esp as a religious observance

noun

1. an act or period of fasting
2. (as modifier): a fast day

Etymology: Old English fæstan; related to Old High German fastēn to fast, Gothic fastan

ˈfaster noun