Green’s Dictionary of Slang

1. a fool.

1776		‘The Battle of Brooklyn’ in Meserve & Reardon Satiric Comedies (1969) 90: Lord! – mem, did he not make codfish of them all at Boston!
1825		‘The Jolly Fisherman’ Universal Songster I 133: Fish, just like men, I’ve often caught, / Crabs, gudgeons, poor John, codfish.
1842		letter in R.B. Hayes Diary in Williams Diary and Letters (1922) I 106: We had silly ladies and weak lemonade [...] ill calculated to enliven the spirits of the ‘codfish’ of Kenyon.

2. (also coddy) one who thinks themselves superior to their peers; also attrib.

c.1850		F.M. Whitcher Widow Bedott Papers (1883) 113: I’ve noticed that yer codfish gentility always dew.
1851		Western Police Gaz. (Cincinnati, OH) 29 Mar. n.p.: [I] will only [...] make a few enquiries in relation to the actions of several bucks and coddies [ibid.] When do you expect to renounce your apish manners and codfish mimickings.
1853		N.Y. Clipper 23 July 2/4: At the opera, the aristocracy, codfish and all other kinds [etc] .
1856		G.G. Foster N.Y. by Gas-Light (1990) 172: And why need we look farther for the causes of that deep-seated hostility to the ‘codfish aristocracy’ which rolls its carriage-wheels over his toes and raises a cloud of dust in his eyes?
1857		Life in Boston & N.Y. (Boston, MA) 11 Apr. n.p.: The ladies of our upper tendom of the tribe codfish , are now in their element.
1865		Daily Tel. 4 Dec. 5/6: A few of the codfish, shoddy, and petroleum aristocracy.
1876		J. Miller First Fam’lies in the Sierras 49: He allers was a kind of a prayin’ codfish eatin’ cuss.
1882		Nat. Police Gaz. (NY) 2 Sept. 2/3: Oscar [Wilde] holds his ground well [...] even though the great Americasn codfish aristocracy frown.
1908		Magnet 22 Feb. 10: Shut up, you greedy young codfish!
1912		J. Stephens Charwoman’s Daughter 184: She saw him as a codfish with a malignant eye.
1934		W.R. Burnett Goodbye to the Past 7: The Old Man shouted [...] that ‘all the goddam codfish aristocrats in Midland City were moving out to Fairhaven and he’d be hanged if he wanted to live in among a lot of real estate salesmen and bank cashiers and riffraff like that’.