The western capercaillie (Tetrao urogallus), also known as the Eurasian capercaillie, wood grouse, heather cock, cock-of-the-woods, or simply capercaillie , is a heavy member of the grouse tribe and the largest of all extant grouse species. Found across Europe and the Palearctic, this primarily-ground-dwelling forest grouse is renowned for its courtship display. The bird shows extreme sexual dimorphism, with males nearly twice the size of females. The global population is listed as "least concern" under the IUCN, The genus name is a Latin word that was used for both the black grouse and the western capercaillie. The specific epithet urogallus is a Neo-Latin partial homophone of German Auerhuhn, a western capercaillie. The word had been used in 1555 by the Swiss naturalist Conrad Gessner in his Historiae animalium.
The common name capercaillie is a corruption of the Scottish Gaelic capall coille () "Horse of the woodland". The Scots borrowing is spelled capercailzie (the Scots use of z represents an archaic spelling with yogh and is silent;