What does "fast" mean?

1. (quick or rapid) moving or happening at high speed. 2. (ahead of time) showing a time that is later than the real time. 3. (firmly fixed) attached firmly so that it cannot move. 4. (quickly) at high speed. 5. (deeply asleep) completely or deeply, usually used with the word 'asleep'. 6. (to abstain from food) to eat little or no food for a period of time, often for religious or medical reasons. 7. (period of not eating) a period of time when you do not eat food.

fast — meaning, definition & examples

Q: Is it correct to say "He ran very fastly to catch the bus."?

No — say "He ran very fast to catch the bus.". The word 'fast' is both an adjective and an adverb; 'fastly' is not a word in modern English.

Word

01quick or rapid

A1 · Beginner

adj. moving or happening at high speed.

adj. characterised by high speed; capable of rapid movement or action.

“The fast train to London takes less than two hours.”

“The company's fast growth surprised many investors who had expected a much slower entry into the European market.”

Synonyms

quick rapid swift

Antonyms

slow

02ahead of time

B1 · Intermediate

adj. showing a time that is later than the real time.

adj. indicating a time ahead of the actual or correct time, typically in reference to a clock or watch.

“My watch is five minutes fast, so I always arrive early for meetings.”

“He intentionally kept his alarm clock ten minutes fast to ensure he never missed the early morning commute.”

Synonyms

ahead

Antonyms

slow

03firmly fixed

B2 · Upper Intermediate

adj. attached firmly so that it cannot move.

adj. firmly fixed or attached; secure against movement or displacement.

“Make sure the knot is fast before you start climbing.”

“The tradition remains fast in the rural provinces, despite the rapid modernisation occurring in the capital city.”

Synonyms

secure fixed stable

Antonyms

loose

04quickly

A1 · Beginner

adv. at high speed.

adv. at a high rate of speed; rapidly.

“You are driving too fast for this narrow road.”

“The news spread fast across the small town, reaching almost every household before the official announcement was made.”

Pitfall

He ran very fastly to catch the bus.

He ran very fast to catch the bus.

The word 'fast' is both an adjective and an adverb; 'fastly' is not a word in modern English.

Synonyms

quickly rapidly

Antonyms

slowly

05deeply asleep

B1 · Intermediate

adv. completely or deeply, usually used with the word 'asleep'.

adv. completely or soundly; almost exclusively used in the collocation 'fast asleep'.

“The baby was fast asleep in her cot after the long walk.”

“Exhausted by the day's hike, the travellers were fast asleep long before the storm began to rattle the cabin windows.”

Synonyms

deeply soundly

06to abstain from food

B2 · Upper Intermediate Medicine

v. to eat little or no food for a period of time, often for religious or medical reasons.

v. to abstain from all or some kinds of food or drink, especially as a religious observance or for medical purposes.

“Patients must fast for twelve hours before having the blood test.”

“Many cultures require followers to fast during specific holy months to demonstrate spiritual discipline and empathy for the poor.”

Synonyms

diet abstain

Antonyms

feast eat

07period of not eating

B2 · Upper Intermediate Countable noun Religion

n. a period of time when you do not eat food.

n. an act or period of fasting.

“He broke his three-day fast with a small bowl of soup.”

“The community gathered for a large celebration to mark the end of the traditional religious fast.”

Synonyms

abstinence

“At the top end of sport, even faster times are imminent: shoe brands will aim to catch up to Adidas’ new gold standard, races will pay big money to have fast athletes line up and challenge each other to new records and athletes themselves may redefine what they think is possible.”

The Globe and Mail 28 Apr 2026

“She was ahead of the record pace at 35km and is a renowned fast finisher - but began to suffer clear discomfort and”

BBC Sport 31 Oct 2025

From Proto-Germanic fastuz, via Proto-West Germanic fast and Old English fæst ("firm, secure"), the word entered Middle English as fast and fest with the core sense of fixedness and security.

The shift to "rapid" appears to have begun in the adverb and only later transferred to the adjective, a pattern comparable to hard in "to run hard". The original sense of "secure, firm" now survives chiefly in fasten and in slightly archaic usage.

The semantic trajectory has parallels elsewhere: Latin rapiō ("to snatch") yielded rapidus ("rapid, quick"), and Irish sciob ("to snatch") produced sciobtha ("quick"). Snatching and speed, it seems, share a conceptual border.

From Old English fæste, formed from fæst with the adverb-forming suffix -e, itself the source of Middle English fast and faste.

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. The religious sense appears to have entered via the Gothic church: Gothic 𐍆𐍰𐍃𐍄𐌰𐌽 (fastan, "hold fast to the rule of abstinence") glossed Greek νηστεύω (nēsteúō) and Latin ieiuno, though the Gothic carried a connotation of holding firm that the Greek and Latin lacked. This semantic development is unique to Gothic.

The Old English noun originally meant "fortress, enclosure"; the religious sense arrived only in late Old English, perhaps under Old Norse influence. Old High German fasta likely existed by the 8th century, shifting to neuter fasten in the 9th — whence modern German Fasten. The medical and weight-reduction senses are recent: mid-1970s, back-formed from the verbal noun fasting in that sense (1960s).

From Middle English faste and 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"), and Gothic 𐍆𐌰𐍃𐍄𐌿𐌱𐌽𐌹 (fastubni, "fasting"). Possibly merged with Old Norse fasta ("fast, fasting"), whence also Danish faste and Swedish fasta.