black·head (bl?k?h?d?)n.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.American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.blackhead (?blæk?h?d) n1. (Pathology) a black-tipped plug of fatty matter clogging a pore of the skin, esp the duct of a sebaceous gland. Technical name: comedo 2. (Veterinary Science) an infectious and often fatal disease of turkeys and some other fowl caused by the parasitic protozoa Histomonas meleagridis. Technical name: infectious enterohepatitis 3. (Animals) any of various birds, esp gulls or ducks, with black plumage on the headCollins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014black?head (?blæk?h?d) n. 1. a small, black-tipped fatty mass in a skin follicle, esp. of the face; comedo. 2. any of several birds having a black head. 3. an intestinal and liver disease of turkeys, chickens, and related birds, caused by the protozoan Histomonas meleagridas, often darkening the skin of the head. [1650?60] Random House Kernerman Webster’s College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.