—adv.
1 a for what reason or purpose (why did you do it?; I do not know why you came). b on what grounds (why do you say that?).
2 (prec. by reason etc.) for which (the reasons why I did it).
—int. expressing:
1 surprised discovery or recognition (why, it's you!).
2 impatience (why, of course I do!).
3 reflection (why, yes, I think so).
4 objection (why, what is wrong with it?).
—n. (pl. whys) a reason or explanation (esp. whys and wherefores).
Phrases and idioms:
why so? on what grounds?; for what reason or purpose?
Etymology: OE hwi, hwy instr. of hwaeligt WHAT f. Gmc
Useful english dictionary. 2012.