Detective to bird to strikebreaker to informer


My friendly bus driver asked, “Where does a word like fink come from?”
Scholars don’t really know the answer to that question, but they’ve made a couple of guesses. 
One popular suggestion links the word to the Pinkerton Detective Agency.
Allan Pinkerton was an undercover agent for the U.S. North during the American Civil War. Following the war, he founded a detective agency which became infamous for using its employees as strike-breakers. This activity began during the so-called 1892 Homestead Strike against Carnegie Steel.
Union members supposedly labeled Pinkerton’s men as “pinks,” a shortened form of Pinkerton. Pinks was soon mispronounced as “finks.”
Many word detectives disagree, believing fink to be lifted from the German word der Fink (finch). Der Fink was applied to any university student who wouldn’t join dueling and drinking associations. In colloquial German, the word has been extended to der Schmierfink (despicable person; dirty fellow).
The German explanation seems likeliest to me. After all, “canary,” often used for “goldfinch,” is yet another word for someone who “sings” on his mates.
Whichever guess is correct, fink isn’t an ancient word, having arrived in English only in the late 19th century. The Oxford Dictionary of Slang dates it to1894 and labels it U.S. slang.
But remember that in the beginning, fink was strictly part of union jargon.
American Slang acknowledges this history and traces fink’s evolution from a noun meaning “strike-breaker” (1890s), to 1902 when it referred to a person loyal to the employer rather than the union. At this time, fink had also come to mean “company spy,” perhaps again evoking Pinkerton’s. By 1925, fink was applied to police officers, detectives, guards and other officials opposing union action. In the 1920s, fink’s current meaning of “informer; stool pigeon,” surfaced as underworld slang.
Usage has continued to advance. No longer only union jargon, we now hear fink used for anyone who is an object of scorn. Here’s an excerpt from an undated issue of Business Month: “It is no secret that most senior executives are contemptuous of whistleblowers, labeling them ‘snitches’ and ‘finks.’”
Nelson Canadian defines fink as, “a hired strike-breaker,” but a new term arose in the 1960s. Rat Fink originated as teen slang, meaning “a treacherous, disgusting person.” As a verb, often used with “on,” to fink means, “to inform on.”
We cannot research fink without encountering its synonym, scab.
Scab is 200 years older than fink insofar as “strike-breaker” is concerned. Scab entered English in the late 16th century as “an unpleasant person.” Its meaning journeyed through “prostitute” (17th century), “constable” (17th to 18th centuries), and finally to “strike-breaker” (1790s). In 1792, a contributor to Early English Trade Unions wrote that a scab “is to his trade what a traitor is to his country.”
Let’s give American author, Jack London (1876-1916), the last word: “After God finished the rattlesnake, the toad and the vampire, He made a scab. A scab is a two-legged animal with a corkscrew soul, a waterlogged brain, and a backbone made of jelly and glue.”