Definition of "blackhead" []

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

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

• "Extractions of active acne whether it is the pustule type we call a pimple or a comedone, which we refer to as a blackhead are tricky and unnecessary and can be unsafe too."
• "When open, the plug is called a blackhead, closed, a whitehead."
• "The deeply-entrenched secretion then goes through a process of chemical change, making it appear black (what we know as "blackhead")."