When is Old English hwænne, with the hw- that scribes later wrote as wh-. It belongs to the tight family of English question words — what, when, where, why, which, who — all descended from an Indo-European stem that supplied relative and interrogative pronouns, and all corresponding to Latin words in qu-: quom, quid, qui.
That correspondence is a useful thing to hold on to, because it shows the same ancestor producing hw- in Germanic and qu- in Latin. When English later borrowed Latin words in qu-, and when Norman scribes respelled native cw- as qu-, the language ended up with question words in wh- and borrowed words in qu- that are, at the deepest level, relatives. The conjunction use is late Old English; asking "at what time?" is recorded from the early 1200s, and say when only from 1889.
when (adv., conj.) Middle English whanne , Old English hwænne , hwenne , hwonne , from Proto-Germanic *hwan- (source also of Old Saxon hwan , Old Frisian hwenne , Middle Dutch wan , Old High German hwanne , German wann "when," wenn "if, whenever"), from pronominal stem *hwa- , from PIE root *kwo- , stem of relative and interrogative pronouns. Equivalent to Latin quom , cum . As a conjunction in late Old English, "at the time that; at the same time that." Interrogatory use, "at what time?" is by early 13c. Non-temporal use, "in which case," is by early 15c. Say when "tell me when to stop pouring this drink" is from 1889.
when came in through Old English, and its spelling follows that family's conventions.
How that family writes these sounds
| /w/ at the start of a question word | wh-what, when, whale |
What gives it away on the page
| wh- | Old English spelled it hw-; the scribes flipped the pair.what, when, whale |
Old English in the spelling guide · guess another word's family