Etymology
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fink (n.)
1902, of uncertain origin, possibly from German Fink "a frivolous or dissolute person," originally "a finch" (see finch); the German word also had a sense of "informer" (compare 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.
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rat fink (n.)
also ratfink, 1963, teen slang, see rat (n.) + fink (n.). Popularized by, and perhaps coined by, U.S. custom car builder Ed "Big Daddy" Roth (1932-2001), who made a hot-rod comic character of it, supposedly to lampoon Mickey Mouse.
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finch (n.)
common European bird, Old English finc "finch," from Proto-Germanic *finkiz "finch" (source also of Middle Low German and Middle Dutch vinke, Dutch vink, Old High German finco, German Fink), perhaps imitative of the bird's note (compare Breton pint "chaffinch," Russian penka "wren").
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