The Collaborative International Dictionary of English v.0.48:

Lesbian \Les"bi*an\ (l[e^]z"b[i^]*an), a.
   1. Of or pertaining to the island anciently called Lesbos,
      now Mitylene, in the Grecian Archipelago.
      [1913 Webster]

   2. Amatory; erotic; -- in allusion to the reputed sensuality
      of the Lesbian people and literature; as, Lesbian novels.
      [archaic]
      [Webster 1913 Suppl.]

   3. Homosexual; -- applied to female homosexuals.
      [PJC]

The Collaborative International Dictionary of English v.0.48:

Lesbian \Les"bi*an\ (l[e^]z"b[i^]*an), n.
   A female homosexual.

   Syn: dyke[vulgar, deprecatory]. [PJC]

WordNet (r) 3.0 (2006):

lesbian
    adj 1: of or relating to or characterized by homosexual
           relations between woman [syn: lesbian, sapphic]
    n 1: a female homosexual [syn: lesbian, tribade, gay
         woman]
    2: a resident of Lesbos