Green’s Dictionary of Slang

a supplier of private loans at maximum interest.

1905		‘Doss Chiderdoss’ ‘An Improved Understanding’ Sporting Times 14 Jan. 1/4: We each trust one another, we’re both thoroughbred; / I’m hard up for a fiver, and loan sharks I dread.
1914		Amer. Mag. 77 June 31–5: Opium is like the salary loan shark — a friend to-day, smoothing difficulty and trouble with a free and easy hand. Tomorrow it becomes a master, exacting a toll a hundredfold more terrible than the ills it eased.
1920		S. Lewis Main Street (1921) 46: He had been called many things – loan-shark, skinflint, tightwad, pussyfoot – but he had never before been called a flirt.
1936		C. Sandburg People, Yes 40: The loan shark victims.
1949		N. Algren Man with the Golden Arm 264: Just like goin’ by the loan shark ’n gettin’ enough to pay off all the little debts with one big one.
1955		B. Schulberg On the Waterfront (1964) 110: The loan-shark leaned forward over Pop’s shoulder.
1966		M. Braly It’s Cold Out There (2005) 192: You ain’t making no loan shark out me.
1973		G.V. Higgins Digger’s Game (1981) 65: Some loan shark.
1989		M. Amis London Fields 179: He had been borrowing money from a loanshark called Kirk Stockist.
1992		K. Lette Llama Parlour 231: I borrowed the final two grand from a goddamned loan shark.
1996		P. Beatty White Boy Shuffle 84: A strong-arm man-child for a loan shark.
2003		A.N. LeBlanc Random Family 247: He risked encountering people he owed money to [...] Delilah, the loan shark.
2010		(con. 1973) C. Stella Johnny Porno 31: Between the money he owed a load shark, his betting losses, and living expenses, Louis needed a score.
2017		A. Parks Bloody January 60: Losing a tally book wasn’t good [...] For a loan shark like Cooper it was the equivalent of the Bible.
2019		D. Winslow Border [ebook] Cirello’s in deep to loan sharks.