cathead, n. — Green’s Dictionary of Slang

cathead n.

[SE cathead, a large biscuit eaten in the US; he or she has no more brains than a biscuit]

(US) a fool.

1953

S. Bellow Augie March (1996) 29: My marks showed it, and the old lady give me a going-over when I brought them in, calling me ‘cat-head’ and in her French, ‘meshant.’.