twat n.

female pudendum, 1650s, of unknown origin. A general term of abuse since 1920s.

The T-word occupies a special niche in literary history, however, thanks to a horrible mistake by Robert Browning, who included it in 'Pippa Passes' (1841) without knowing its true meaning. 'The[n] owls and bats,/Cowls and twats,/Monks and nuns,/In a cloister's moods.' Poor Robert! He had been misled into thinking the word meant 'hat' by its appearance in 'Vanity of Vanities,' a poem of 1660, containing the treacherous lines: 'They'd talk't of his having a Cardinalls Hat,/They'd send him as soon an Old Nuns Twat.' (There is a lesson here about not using words unless one is very sure of their meaning.) [Hugh Rawson, "Wicked Words," 1989]

Browning composed in deliberately audacious meters that required words in all sizes and shapes, and he reached back in time for diction, forgetting here the Victorian critics' warning of the 17th century's coarseness.