Medicine A plug of keratin and sebum within a hair follicle that is blackened at the surface. Also called comedo.
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.
Any of various birds, such as the scaup, with dark head markings.
(blāk'hěd') 