Green’s Dictionary of Slang

stupid, foolish; a term of abuse.

1926		(con. 1918) L. Nason Chevrons 72: This nit-wit officer we got.
1936		‘George Orwell’ Keep The Aspidistra Flying (1962) 70: The pink doll-faces of upper-class women gazed at him [...] Bloody nit-witted lapdogs.
1937		H.C. Brown A Mind Mislaid 139: His slanting chin and shifty eyes strongly resemble the familiar features of this ‘nitwit’ son of a ‘nitwit’ father.
1942		A. Christie Body in the Library (1959) 83: That half-baked nitwitted little slypuss.
1958		A. Sillitoe Sat. Night and Sun. Morning 18: My hands would be round his throat first, the nit-witted, dilat’ry, unlucky bastard.
1960		‘Hergé’ Tintin and the Red Sea Sharks 9: You thundering nitwitted numskull you!
1961		M. Braly Felony Tank (1962) 8: Goddam nitwit kids!
1963		B. Hecht Gaily, Gaily 42: MacArthur was a nitwitted card player.
1972		D. Jenkins Semi-Tough 20: She’s such a self-centered, spoiled bitch with that nitwit accent and her shitheel parents.
1985		G. Story Need of Wanting Always 149: And some nitwit baby, likely, taking shape inside her.
1990		S. Morgan Homeboy 67: In all the hubbub and hoopla some nitwit cop had misplaced the goddam five-pound nickelplated padlock.
2004		‘H.U. Quickwit’ Plagiarizm: How Profs Spot a Cheat 124: The assignments from the dimwit and nitwit category professors don’t really deserve any student’s time.