comedo

[Latin comedō, glutton (from a comparison of the worm-like shape of the waxy material that can be squeezed from a blackhead to a worm believed to feed on the body), from comedere, to eat up : com-, intensive pref.; see com- + edere, to eat.]

A blackhead and the primary lesion of acne vulgaris.

Pl. comedones; a blackhead; a plug of keratin and sebum within the dilated orifice of a hair follicle frequently containing bacteria. Found in feline and canine acne, hyperadrenocorticism, Schnauzer comedo syndrome (see below).

• Schnauzer c. syndrome — a condition in which numerous comedones form in the skin over the back of certain predisposed Schnauzer dogs, usually of the miniature variety. The cause is unknown but believed to be an inherited disorder of keratinization.

The noun has one meaning:

Meaning #1: a black-tipped plug clogging a pore of the skin
  Synonym: blackhead