fink

See also: Fink

Unknown; first attested in 1894.^[1] A connection to Yiddish as some propose is unlikely.^[2]

Suggested origins include:

German Fink (“finch; frivolous or dissolute person; informer”) as finches are notoriously chatty birds in groups. If so, then Doublet of finch. Compare canary (“informer”).
Partly from the German theory, a fanciful association by students with the freedom of wild birds as opposed to caged ones.
The slang name pink for Pinkerton agents and their use as strikebreakers in the 1892 Homestead strike. If the term is from the corporate name, then it is of Scots origin, Pinkerton being from a place near Dunbar, which is from an unrecognized first element (possibly ultimately pre-Celtic substrate) and Old English tun (“enclosure, homestead, etc.”).

fink (plural finks)

informer

strikebreaker

fink (third-person singular simple present finks, present participle finking, simple past and past participle finked)

(chiefly US, slang) To betray a trust; to inform on.
- 1952, Ralph Ellison, Invisible Man, Penguin Books (2014), page 222:
  “I move that we determine through a thorough investigation whether the new worker is a fink or no; and if he is a fink, let us discover who heʼs finking for!”

to betray a trust

fink (third-person singular simple present finks, present participle fought, simple past and past participle fought)

fink (plural finks)

(South Africa) Any of several birds in the family Ploceidae native to southern Africa.

[1]
“Stumpy” and Other Interesting People by George Ade published on the 17th of March 1894 in the Chicago Record in the column Stories of the Streets and of the Town. A criminal character describes it as similar to "a stiff, a skate. [Someone who] drinks and never comes up. [Someone who's] always layin' to make a touch, too."
[2]
Studies in Etymology and Etiology by David L. Gold, page 77/Section 5

“fink”, in Dictionary.com Unabridged, Dictionary.com, LLC, 1995–present.
"fink" in Cambridge Advanced Learner's Dictionary (Cambridge University Press, 2007)
"fink" in the Dictionary of South African English
“fink”, in Lexico, Dictionary.com; Oxford University Press, 2019–2022.
Oxford English Dictionary, second edition (1989)
Random House Webster's Unabridged Electronic Dictionary (1987-1996)

From Proto-Albanian *spinga, from Proto-Indo-European *(s)pingos (“chaffinch”), identical with Greek σπίγγος (spíngos, “id”), English spink, Old Norse spiki (“kind of bird”). One might also consider a borrowing from Proto-Germanic *finkiz, *finkōn (“finch”), possibly Balkan Gothic.