At one's wit's end
What's the meaning of the phrase 'At his wit's end'?
To be at your wit's end is to be perplexed; unable to think what to do.
What's the origin of the phrase 'At his wit's end'?
The earliest text that refers to people being at their wit's end is William Langland's Middle English narrative poem The vision of William concerning Piers Plowman, 1370-90:
Astronomyens also aren at hir wittes ende.
[Astronomers are also at their wit's end.]
By 'wit' Langland didn't mean the facility to deliver sparkling and amusing dialogue, like Oscar Wilde or Noel Coward. The wit in 'wit's end' was a more general mental facility.
Langland had described a situation that was perplexing to all-comers, both "those of the flood and the land - shipmen and shepherds" and that, even those who look outside our world (astronomers), didn't know what to do.
The expression also appears later in the Bible, Psalms 107:27 (King James Version):
They reel to and fro, and stagger like a drunken man, and are at their wit's end.