comedo

from WordNet (r) 3.0 (2006)

comedo
    n 1: a black-tipped plug clogging a pore of the skin [syn:
         {blackhead}, {comedo}]

from The Collaborative International Dictionary of English v.0.48

Comedo \Com"e*do\, n.; pl. {Comedones}. [L., a glutton. See
   {Comestible}.] (Med.)
   A small nodule or cystic tumor, common on the nose, etc.,
   which on pressure allows the escape of a yellow wormlike mass
   of retained oily secretion, with a black head (dirt).
   [1913 Webster]