beggars belief

[Vespervaldez]

meaning

[Quizmonster]

'Beggar' - used as a verb, as it is in this phrase, rather than a noun - dates from the 1500s. It means 'to make a beggar of'. The earliest use of a phrase developing this point was in Shakespeare's 'Antony and Cleopatra' (probably 1607). He wrote: "For her own person it beggared all description", talking of the lady herself. Later versions were 'it beggars compare' and even the children's card-game 'beggar-my-neighbour' which appeared in the 1700s. 'Beggars belief', specifically, obviously came onto the scene at some point along the historic line, together with 'beggars comprehension' and a variety of others.

[Quizmonster]

Perhaps I should have added to my above answer that the idea lying behind the phrase is that the thing under consideration is so utterly incredible that there would seem to be no way one could possibly believe it. Nevertheless, it does turn out to be true.