the ermine in its brown summer coat with black-tipped tail
Mustela erminea, the ermine or short-tailed weasel, a mustelid native to Eurasia and North America, distinguished from the least weasel by its larger size and longer tail with a prominent black tip.
The word "stoat" comes from Middle English stote, which originally meant the ermine, particularly when wearing its brown summer coat. Its exact origins are uncertain, though it may be related to Old Norse words for a bull or steer.