Source : Webster's Revised Unabridged Dictionary (1913)

Stoat \Stoat\, n. [OE. stot a stoat, horse, bullock; perhaps
   originally only of male animals, and akin to D. stooten to
   push, E. stutter; cf. Icel. st?tr a bull, Sw. stut a bullock.
   Cf. {Stot}.] (Zo["o]l.)
   The ermine in its summer pelage, when it is reddish brown,
   but with a black tip to the tail. The name is sometimes
   applied also to other brown weasels.

Source : WordNet®

stoat
     n : the ermine in its brown summer coat with black-tipped tail