The Collaborative International Dictionary of English v.0.48:

Catamite \Cat"a*mite\ (k[a^]t"[.a]*m[imac]t), n. [L. Catamitus,
   an old form of Ganymedes Ganymede, Gr. Ganymh`dhs.]
   A boy kept for unnatural purposes.
   [1913 Webster]

WordNet (r) 3.0 (2006):

catamite
    n 1: a boy who submits to a sexual relationship with a man