You want me to find out what happened to all those kids I ran with, who didn't know I was studying them like bugs in a bottle. You want me to go down there seventeen years later and say, "I'm the guy finked on you, remember me?"
-- Harlan Ellison, "Punky and the Yale Men," Love Ain't Nothing But Sex Misspelled, 1968
He held out for a while, laid low, and then, when the ranks started to break, he finked and crossed the picket lines.
-- Allen Barra, "Joe Montana: Tarnished Hero," Big Play: Barra on Football, 2004
Fink emerged as a slang term in the US in the early 1900s. Its origin is unknown, but some etymologists cite the German word of the same spelling, which means "a frivolous or dissolute person," as a possible lexical ancestor.