The word 'whither' originates from the Old English 'hwider', a variant of 'hwæder', meaning 'to what place'. It is built from the Proto-Germanic interrogative base 'hwa-' (who, what) combined with a comparative suffix '-der-', indicating direction or motion towards. This formation is parallel to 'hither' (to this place) and 'thither' (to that place). Over time, its function was largely absorbed by the more general 'where', rendering 'whither' archaic or literary in modern English, used primarily to evoke a formal or poetic tone when questioning a destination or end point.

This word is a simplex form derived from Old English. It is an unsegmentable interrogative adverb in its modern spelling.