What is "horse of the wood"

Capercailzie \Ca"per*cail`zie\, or Capercally \Ca"per*cal`ly\, n. [Gael, capulcoile.] (Zo["o]l.) A species of black Old World grouse ( Tetrao uragallus) of large size and fine flavor, found in northern Europe and formerly in Scotland; -- called also cock of the woods and horse of the wood. [Written also capercaillie, capercaili.]

n. large black Old World grouse [syn: capercaillie, capercailzie, Tetrao urogallus]