why

American  

[hwahy, wahy] / ʰwaɪ, waɪ /

adverb

1. for what? for what reason, cause, or purpose?.

   Why did you behave so badly?

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conjunction

1. for what cause or reason.

   I don't know why he is leaving.

2. for which; on account of which (usually after reason to introduce a relative clause).

   the reason why he refused to go.

3. the reason for which.

   That is why he returned.

noun

whys plural

1. a question concerning the cause or reason for which something is done, achieved, etc..

   a child's unending hows and whys.

2. the cause or reason.

   the whys and wherefores of a troublesome situation.

interjection

1. (used as an expression of surprise, hesitation, etc., or sometimes a mere expletive).

   Why, it's all gone!

why British  

/ waɪ /

adverb

1. 1. for what reason, purpose, or cause?

      why are you here?

   2. ( used in indirect questions )

      tell me why you're here

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pronoun

1. for or because of which

   there is no reason why he shouldn't come

noun

1. (usually plural) the reason, purpose, or cause of something (esp in the phrase the whys and wherefores )

interjection

1. an introductory expression of surprise, disagreement, indignation, etc

   why, don't be silly!

Usage

See reason.

Other Word Forms

Inflected Forms

noun

• whys
  plural

Etymology

Origin of why

First recorded before 900; Middle English; Old English hwī, hwȳ, instrumental case of hwæt what; cognate with Old Norse hvī

Example Sentences

"And it's basically a sea of ions, which is why we base our technology around it, so we can pull those ions out into an electrospray."

From Science Daily • Jun. 10, 2026

“That’s my gut. And I feel like that’s what happened to us on Caruso and possibly why he didn’t run” for governor this year.

From Los Angeles Times • Jun. 10, 2026

This is why the nation’s founders instituted religious freedom — they witnessed how Europe was torn apart by wars waged between different flavors of Christianity.

From Salon • Jun. 10, 2026

That's why, in his decree, Zelensky said he was using the UPA's name "with the aim of restoring the historical traditions of the national army".

From BBC • Jun. 10, 2026

Is that why he kept badgering me to get Jillian here tonight?

From "Legendary Frybread Drive-In" by Cynthia Leitich Smith