Old English hwæt , from Proto-Germanic *khwat (cf. Old Saxon hwat , Old Norse hvat , Danish hvad , Old Frisian hwet , Dutch wat , Old High German hwaz , German was , Gothic hva "what"), from PIE *qwod , neuter singular of *qwos "who" (see who ).
Meaning "what did you say?" is recorded from ; as an interrogative expletive at the end of sentences it is first recorded 1785, common early 20c. in affected British speech. Or what as an alternative end to a question is first attested 1766. "To give one what for is to respond to his remonstrant what for? by further assault" [Weekley]. The phrase is attested from 1873. What's-his-name for "unspecified person" is attested from 1690s; variant whatsisface is first recorded 1967. What's up? "what is happening?" first recorded 1881.