weasel

noun, plural wea·sels, (especially collectively) wea·sel.

1. any small carnivore of the genus Mustela, of the family Mustelidae, having a long, slender body and feeding chiefly on small rodents.
2. any of various similar animals of the family Mustelidae.
3. a cunning, sneaky person.
4. a tracked vehicle resembling a tractor, used in snow.
5. Slang. an informer; stool pigeon.