The word 'when' traces its lineage directly back to the Old English interrogative adverb 'hwanne' or 'hwenne', which itself evolved from the Proto-Germanic interrogative base 'hwan-'. This base is related to the Proto-Indo-European interrogative stem 'kʷo-', which also gave rise to other English question words like 'what', 'where', and 'who'. The core semantic function of asking about time has remained remarkably consistent from its ancient roots. Over centuries, its usage expanded from a simple interrogative to encompass relative, conjunctive, and nominal functions, solidifying its role as a fundamental temporal marker in the English language.

This is a simplex word of Germanic origin. It functions as an interrogative and relative adverb, conjunction, pronoun, and noun.