Fail Definition

fāl

failed, failing, fails

verb

failed, failing, fails

To be lacking or insufficient; fall short.

The water supply is failing.

Webster's New World

To be unsuccessful.

An experiment that failed.

American Heritage

To lose power or strength; weaken; die away.

Webster's New World

To be unsuccessful in being acted upon.

An idea that failed to be accepted by the board.

American Heritage

To stop operating or working.

The brakes failed.

Webster's New World

Synonyms:

Antonyms:

noun

fails

Failure.

Webster's New World

A failing grade.

The student received a fail on the final paper.

American Heritage

(slang, US) A failure (something incapable of success)

Wiktionary

Synonyms:

adjective

(slang, US) That is a failure.

Wiktionary

Synonyms:

idiom

without fail

With no chance of failure:
Be here at noon without fail.

American Heritage

fail of

to fail to achieve; be without

Webster's New World

Other Word Forms of Fail

Noun

Singular:

fail

Plural:

fails

Idioms, Phrasal Verbs Related to Fail

Origin of Fail

From Middle English failen, from Anglo-Norman faillir, from Vulgar Latin *fallire, alteration of Latin fallere (“to deceive, disappoint”), from Proto-Indo-European *bʰāl- (“to lie, deceive”). Compare Dutch feilen, falen (“to fail, miss”), German fehlen (“to fail, miss, lack”), Danish feile (“to fail, err”), Swedish fela (“to fail, be wanting, do wrong”), Icelandic feila (“to fail”).

From Wiktionary
Middle English failen from Old French faillir from Vulgar Latin fallīre variant of Latin fallere to deceive

From American Heritage Dictionary of the English Language, 5th Edition