[black.head] n (ca. 1837) 1: a small plug of sebum blocking the duct of a sebaceous gland esp. on the face
2: a destructive disease of turkeys and related birds caused by a protozoan (Histomonas meleagridis) that invades the intestinal ceca and liver
3: a larval clam or mussel attached to the skin or gills of a freshwater fish