What is Old English hwæt, and the modern spelling reverses those first two letters — a scribal habit that also gave us when, where, why, which and whale from hw- originals. The pronunciation did not flip; only the writing did.
The word is one of the oldest things in the language, from an Indo-European stem that supplied relative and interrogative pronouns across the whole family and corresponds exactly to Latin quid. Its exclamatory use — emphasising a response, calling attention, launching a story — was already there in Old English, and famously so: hwæt is the first word of Beowulf, where it functions as something between "Listen!" and a throat-clearing. A word doing that job in the eighth century and still doing it now is about as good an illustration of native core vocabulary as English offers.
what (pron., adv.) interrogative pronoun, Old English hwæt , referring to things in abstraction; also "why, wherefore; indeed, surely, truly," from Proto-Germanic pronoun *hwat (source also of Old Saxon hwat , Old Norse hvat , Danish hvad , Old Frisian hwet , Dutch wat , Old High German hwaz , German was , Gothic hva "what"), from PIE *kwod , neuter singular of *kwos "who," from PIE root *kwo- , stem of relative and interrogative pronouns. Corresponding to Latin quid . As an adjective and adverb in Old English, lending interrogative force. As a conjunction in late Old English. Exclamatory use, emphasizing the speaker's emotional response, calling attention, or introducing a narrative, was in Old English. It is the first word in "Beowulf." What, ho! as an exclamation or summons is by late 14c. What the _____ ( devil , etc.) as an exclamation of surprise is from c. 1400. As an interrogative expletive at the end of sentences by 1785; common in affected British speech. As meaning "what did you say?" from c. 1300. Or what as an alternative end to a question is attested by 1766. What have you "anything else one can think of" is from 1925. What's up? "what is happening?" first recorded 1881. "To give one what for is to respond to his remonstrant what for? by further assault" [Weekley]. The phrase is attested from 1873; what for? "for what reason" is from late 14c., as framing a question, by 1760. To know what is what "understand the qualities or natures of things" is from c. 1400; I'll tell you what to emphasize what is about to be said is in Shakespeare. Middle English also had an interjection whatkinnes "what? what sort of?"
what 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