■ interrogative adverb for what reason or purpose.
■ related adverb (with reference to a reason) on account of which; for which.
↘the reason for which.
■ exclamation
1》 expressing surprise or indignation.
2》 used to add emphasis to a response.
■ noun ( plural ~s ) a reason or explanation.
Origin
OE hwī , hwȳ 'by what cause', instrumental case of hwæt 'what', of Gmc origin.