Fink

noun

an unpleasant or contemptible person.

1. inform on (someone) to the authorities.

   there was no shortage of people willing to fink on their neighbours

2. fail to do something promised or expected.

   administration officials had finked out

   we felt like he finked out on us

late 19th century: of unknown origin; perhaps from German, literally ‘finch’, but also a pejorative term. Students started to refer to non-members of fraternities as finks, probably by association with the freedom of wild birds as opposed to caged ones. The term was later generalized to denote those not belonging to organizations such as trade unions.