Green’s Dictionary of Slang

sop n.

1. a fool, a simpleton.

1859		Hotten Dict. of Modern Sl. etc. 98: sop, a soft or foolish man.
1864, 1867, 1870		Hotten Sl. Dict.
1890–1904		Farmer & Henley Sl. and Its Analogues.
1895		Crowe Aus. Sl. Dict. 78: Sop, a contraction for milksop; a feeble-minded man.
1901		A. Perry [perf. Marie Lloyd] William ’Enry Sarnders 🎵 I broke down and started ‘blubbing’ like a silly sop.
1914		Ade ‘The New Fable of the Father Who Jumped In’ in Ade’s Fables 86: Kenneth was the kind of Sop that you see wearing Evening Clothes on a Colored Post-Card.
1928		R. Hall Well of Loneliness (1976) 44: You’re a dear little sop, that’s what you are!
1945		K. Amis letter 24 Dec. in Leader (2000) 25: I like the sop.
1996		J. Baker Death Minus Zero (1998) 181: The poor sop would still have to do another three hundred and ninety-nine haircuts before he broke even.

2. a drunkard.

1905

Sporting Times 1 Apr. 1/5: The old soaker sitting by the upturned cask in the ‘Jug and Bottle’ [...] groaned ‘An’ ’eavy an’ ’orrible blow!’ ‘Wot is?’ enquired a brother sop.

In compounds

sophead (n.) [-head sfx (1)]

a fool, a simpleton.

2001

A. Kapp in Daily Collegian (US) 24 Sept. 🌐 I’ve been told to ‘grow-up,’ been called ‘unpatriotic,’ ‘un-American,’ a ‘sophead’ (which I’m still trying to figure out, by the way), and a ‘traitor.’.