- a black or brown-speckled seabird of the genus Cepphus, of northern seas, having a sharply pointed black bill, red legs, and white wing patches, as C. grylle(black guillemot ), of the North Atlantic Ocean and the similar C. columba(pigeon guillemot ) of the North Pacific Ocean.
- a murre of the genus Uria.
- any northern oceanic diving bird of the genera Uria and Cepphus, having a black-and-white plumage and long narrow bill: family Alcidae (auks, etc), order Charadriiformes
