Stoat, carnivorous mammal of the weasel family. Its slim body is about 30cm long, including the tail, and like others of the family it has short legs and move sinuously. It preys upon rabbits and smaller animals in many temperate and northern parts of the world. In the latter regions its fur turns from reddish-brown and white to white in winter, when it is known as ermine. Family Mustelidae; species Mustela erminea.