1. A skin lesion consisting of a hair follicle that is occluded with sebum and keratin, appearing black at the surface.

2. An infectious disease of turkeys and some wildfowl that is caused by a protozoan (Histomonas meleagridis) and results in lesions of the intestine and liver. Also called enterohepatitis, histomoniasis, infectious enterohepatitis.

3. Any of various birds, such as the scaup, with dark head markings.