Green’s Dictionary of Slang

1. the practice of lending money at usurious rates, esp. by organized crime syndicates.

1953		E. Reid Shame of N.Y. 141: Among the rackets on the piers are: [...] loan-sharking, with the ‘sharks’ charging as high as 500 percent interest.
1969		Salerno & Tompkins Crime Confederation 367: The mechanism of loansharking should adapt very well to electronic banking.
1974		(con. 1945) E. Thompson Tattoo (1977) 293: An offshoot of the gambling was a five-dollar-for-ten-dollar loan-sharking business.
1985		N. Pileggi Wiseguy (2001) 8: He had been arrested for loan-sharking.
1996		S. Frank Get Shorty [film script] harry: Really? You ever been arrested? chili: I’ve been picked up a couple times. Loan sharking. Racketeering. But I was never convicted. I’m clean.
2001		K. Sampson Outlaws (ms.) 32: Al Stanton is not a drug dealer [...] To the best of my knowledge he’s still into loan-sharking.

2. in attrib. use of sense 1.

2001

C. Stella Eddie’s World 149: The dispatcher was one of his loan-sharking cutomers.