fink:
(plural: ‘fink; pronunciation: the letters ‘fi’ rhyme with the letters ‘fi’ in “fill” — for the pronunciation of this word, please click here)

a fink, hated by others
a person who is hated by others;
a person who tells (informs) the police about fellow criminals;
an informer;
a person who is hired (employed) in place of a regular worker on strike; a strikebreaker; a blackleg (to strike, in this context = to stop working in an office, factory, industry, etc. in order to show workers protest against the management about the conditions of work – low pay, bad working conditions, health hazards, etc.),

a fink (police informer) tipping the police
Rob is very arrogant and indecent; it’s no wonder people nicknamed him ‘fink’ and avoid him.
Most of the information about crimes and criminals that the police get is from their finks who are petty thieves themselves but assist the police by passing on information at street level secretly.
The life of rat fink will be very miserable if he’s put in the same prison cell as the other criminals on whom he has tipped off to the police before.
The members of the Finks Gang, a bike-riding club, who love to call themselves ‘finks’, always get in trouble with the law and they are more often in the prisons than on their bikes!
