The Collaborative International Dictionary of English v.0.48:

acne \ac"ne\ ([a^]k"n[-e]), n. [NL., prob. a corruption of Gr.
   'akmh`.] (Med.)
   Inflammation of the sebaceous glands that are associated with
   hair follicles, leading to visible comedones and pimples,
   especially on the face, back, and chest.
   [1913 Webster + AS]

WordNet (r) 3.0 (2006):

acne
    n 1: an inflammatory disease involving the sebaceous glands of
         the skin; characterized by papules or pustules or comedones