Real Dictionary

polecat
countable noun: A polecat is a small, thin, fierce wild animal. Polecats have a very unpleasant smell.

polecat in American English
any of several small, Old World weasels, usually having anal glands that eject foul-smelling fluid when the animal is in danger, esp. one (Mustela putorius) that is known as a “ ferret” when domesticated to kill rats, mice, etc.
noun: a European mammal, Mustela putorius, of the weasel family, having a blackish fur and ejecting a fetid fluid when attacked or disturbed

polecat in British English
noun: a dark brown musteline mammal, Mustela putorius, of woodlands of Europe, Asia, and N Africa, that is closely related to but larger than the weasel and gives off an unpleasant smell