why

From Middle English why, from Old English hwȳ (“why”), from Proto-Germanic *hwī (“by what, how”), from Proto-Indo-European *kʷey, instrumental case of *kʷís (“who”), *kʷid (“what”).

Cognate with Old Saxon hwī (“why”), hwiu (“how; why”), Middle High German wiu (“how, why”), archaic Danish and Norwegian Bokmål hvi (“why”), Norwegian Nynorsk kvi (“why”), Swedish vi (“why”), Faroese and Icelandic hví (“why”), Latin quī (“why”), Doric Greek πεῖ (peî, “where”), Ukrainian чи (čy, “if”), Polish czy, Czech či (“or”), Serbo-Croatian či (“if”). Compare Old English þȳ (“because, since, on that account, therefore, then”, literally “by that, for that”). See thy.

A variant of quey.