1902, of uncertain origin, possibly from German Fink "a frivolous or dissolute person," originally "finch;" the German word also had a sense of "informer" (cf. stool pigeon). The other theory traces it to Pinks, short for Pinkerton agents, the private police force hired to break up the 1892 Homestead strike. As a verb, 1925 in American English slang. Related: Finked; finking.
[origin unknown; perhaps fr Pink, ''a Pinkerton agent engaged in strike-breaking,'' or fr German Fink, ''finch,'' a university students' term for a student who did not join in dueling and drinking societies; first sense said to have been used during the Homestead Strike of 1892; fifth noun sense was unaccountably revived in the early 1960s]