"Finally, erroneous words are sometimes introduced by respected users of the language who simply make a mistake. Shakespeare thought illustrious
was the opposite of lustrous
and thus for a time gave it a sense that wasn't called for. Rather more alarmingly, the poet Robert Browning caused considerable consternation by including the word twat
in one of his poems, thinking it an innocent term. The work was Pippa Passes,
written in 1841 and now remembered for the line 'God's in His heaven, all's right with the world.' But it also contains this disconcerting passage:
Then owls and bats,
Cowls and twats,
Monks and nuns in a cloister's moods,
Adjourn to the oak-stump pantry!
"Browning had apparently somewhere come across the word twat
-- which meant precisely the same then as it does now -- but pronounced it with a flat a
and somehow took it to mean a piece of headgear for nuns. The verse became a source of twittering amusement for generations of schoolboys and a perennial embarrassment to their elders, but the word was never altered and Browning was allowed to live out his life in wholesome ignorance because no one could think of a suitably delicate way of explaining his mistake to him."
-- Bill Bryson,
The Mother Tongue: English and how it got that way