why

UK: /ˈ^hwaɪ/ US: /hwaɪ, waɪ/ ,(hwī, wī)

Inflections of 'why' (n): npl: whys

WordReference Random House Learner's Dictionary of American English © 2026

why /hwaɪ, waɪ/   adv., conj., n., pl. whys, interj. 
adv. 

1. (used to introduce a question) for what cause or reason or purpose?:
   Why do you ask? Why are you here?

conj. 

2. for what cause or reason:
   I don't know why he left.
3. on account of which:
   the reason why she refused.
4. the reason for which:
   That is why he returned.

n. [countable]

5. the cause or reason:
   to figure out the whys and wherefores.

interj. 

6. (used to express surprise, hesitation, or impatience):
   Why, go right ahead! Why, what do you mean?

WordReference Random House Unabridged Dictionary of American English © 2026

why  (hwī, wī), adv., conj., n., pl. whys, interj. 
adv. 

1. for what? for what reason, cause, or purpose?:
   Why did you behave so badly?

conj. 

2. for what cause or reason:
   I don't know why he is leaving.
3. for which;
   on account of which (usually after reason to introduce a relative clause):
   the reason why he refused to go.
4. the reason for which:
   That is why he returned.

n. 

5. a question concerning the cause or reason for which something is done, achieved, etc.:
   a child's unending hows and whys.
6. the cause or reason:
   the whys and wherefores of a troublesome situation.

interj. 

7. (used as an expression of surprise, hesitation, etc., or sometimes a mere expletive):
   Why, it's all gone!

• bef. 900; Middle English; Old English hwī, hwȳ, instr. case of hwæt what; cognate with Old Norse hvī

Usage

See reason. 

Collins Concise English Dictionary © HarperCollins Publishers::

why / waɪ/ adverb

1. for what reason, purpose, or cause?: why are you here?
2. (used in indirect questions): tell me why you're here

pronoun

1. for or because of which: there is no reason why he shouldn't come

noun (whys)

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!

Etymology: Old English hwī; related to Old Norse hvī, Gothic hveileiks what kind of, Latin quī