fast

verb

fasted; fasting; fasts

intransitive verb

1

: to abstain from food

2

: to eat sparingly or abstain from some foods

Examples of fast in a Sentence

She always fasts on Yom Kippur.

Patients must fast for six hours before having the procedure.

Recent Examples on the Web

But research increasingly suggests that exercising after meals, particularly later in the day, may improve blood sugar regulation more effectively than fasted morning workouts. —Ezekiel J. Emanuel, CNBC, 29 May 2026

These Keen boots marked almost $100 off the original price keep you light and fast on your feet. —Olivia Young, Travel + Leisure, 29 May 2026

There is evidence that regular magnesium supplementation can lower fasting blood sugar levels. —Ashley Wong, Health, 29 May 2026

During this period, Muslims around the world engage in intensified devotion by fasting, increasing their voluntary prayers, and reading the Quran. —Andrew R. Chow, Time, 26 May 2026

Word History

Etymology

Middle English, from Old English fæstan

First Known Use

before the 12th century, in the meaning defined at sense 1

Phrases Containing fast

• acid-fast
• fast and furious
• fast and loose
• fast break
• fast-casual
• fast day
• fast fashion
• fast-food
• fast-forward
• fast lane
• fast-pitch
• fast/quick buck
• fast/quick study
• fast-talk
• fast-track
• fast-twitch
• going/getting nowhere fast
• going nowhere fast
• hard-and-fast
• not so fast
• play fast and loose
• pull a fast one
• thick and fast

Rhymes for fast

• bast
• blast
• cast
• caste
• classed
• clast
• gassed
• gast
• glassed
• grassed
• hast
• last

Kids Definition

fast

1 of 4 adjective

ˈfast 

1

a

: firmly fixed or bound

b

: tightly shut

c

: sticking firmly

2

: firmly loyal

became fast friends

3

a

: moving or able to move rapidly

b

: taking a short time

c

: giving quickness of motion (as to a thrown ball)

d

: favorable to speed

the faster route

4

: indicating ahead of the correct time

my clock is fast

5

: tricky and unfair

pulled a fast one

6

: not likely to fade

fast colors

fast

2 of 4 adverb

1

: in a fixed manner

stuck fast

2

: in a complete manner : soundly, deeply

fast asleep

3

: with great speed

a building fast going to ruin

fast

3 of 4 verb

1

: to go without eating

2

: to eat in small amounts or only certain foods

fast

4 of 4 noun

1

: the act of fasting

2

: a time of fasting

Etymology

Old English fæst "firmly fixed"

Old English fæstan "to go without eating"

Medical Definition

fast

1 of 3 adjective

ˈfast 

1

: firmly fixed

2

a

: having a rapid effect

a fast medicine

b

: allowing for the rapid passage of a gas or liquid

3

: resistant to change (as from destructive action)

—used chiefly of organisms and in combination with the agent resisted

acid-fast bacteria

fast

2 of 3 intransitive verb

1

: to abstain from food

2

: to eat sparingly or abstain from some foods

transitive verb

: to deny food to

the patient is fasted and given a mild hypnotic

—Lancet

fast

3 of 3 noun

1

: the practice of fasting

2

: a time of fasting