The word 'whose' originates from Old English 'hwæs', the genitive case of both 'hwā' (who) and 'hwæt' (what). It is part of the ancient Proto-Indo-European interrogative stem kʷo-/kʷi-, which is the source of similar question words across many languages. Over time, 'whose' evolved from its Old English form through Middle English, maintaining its core function of indicating possession in questions and relative clauses. Its modern spelling and pronunciation stabilized by the Early Modern English period, solidifying its role as the standard possessive form for 'who' and 'which'.

The word 'whose' is an unsegmentable simplex word. It is the genitive or possessive form of the interrogative and relative pronouns 'who' and 'which'. Its functional role is as a possessive determiner or pronoun.