Dictionary.com
Thesaurus.com
Synonyms

why

American  
[hwahy, wahy] / ʰwaɪ, waɪ /

adverb

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

    Why did you behave so badly?


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

plural

whys
  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. for what reason, purpose, or cause?

      why are you here?

    2. ( used in indirect questions )

      tell me why you're here

"Collins English Dictionary — Complete & Unabridged" 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

pronoun

  1. for or because of which

    there is no reason why he shouldn't come

"Collins English Dictionary — Complete & Unabridged" 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

noun

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

"Collins English Dictionary — Complete & Unabridged" 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

interjection

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

    why, don't be silly!

"Collins English Dictionary — Complete & Unabridged" 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Usage

See reason.

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

Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.

But she understands why, for many people, doubts remain.

From Los Angeles Times

"Robert always brings mesmerising power and depth to every role. I know viewers will be on the edge of their seats wondering what his character will do next, and why."

From BBC

That’s why the document ends with their mutual pledge of “our Lives, our Fortunes and our sacred Honor.”

From Los Angeles Times

So that’s why I think it’s kind of a good year for the films.

From Los Angeles Times

Ask anyone where L.A.’s Black mecca is and they will more than likely point you to Leimert Park, so it’s understandable why this is a top pick for the gateway to the Historic South L.A.

From Los Angeles Times