Source : Webster's Revised Unabridged Dictionary (1913)

Concubine \Con"cu*bine\, n. [F., fr. L. concubina; con- + cubare
   to lie down, concumbere to lie together, akin to E. cubit.]
   1. A woman who cohabits with a man without being his wife; a
      paramour.

   Note: Concubine has been sometimes, but rarely, used of a
         male paramour as well as of a female. --Trench.

   2. A wife of inferior condition; a lawful wife, but not
      united to the man by the usual ceremonies, and of inferior
      condition. Such were Hagar and Keturah, the concubines of
      Abraham; and such concubines were allowed by the Roman
      laws. Their children were not heirs of their father.

Source : WordNet®

concubine
     n : a woman who cohabits with an important man [syn: {courtesan},
          {doxy}, {odalisque}, {paramour}]