WordNet (r) 3.0 (2006):

homosexuality
    n 1: a sexual attraction to (or sexual relations with) persons
         of the same sex [syn: homosexuality, homosexualism,
         homoeroticism, queerness, gayness]

Moby Thesaurus II by Grady Ward, 1.0:

35 Moby Thesaurus words for "homosexuality":
   active algolagnia, algolagnia, algolagny, amphierotism,
   autoeroticism, bisexuality, coprophilia, exhibitionism, fetishism,
   heterosexuality, homoeroticism, homosexualism, incest,
   incestuousness, lesbianism, masochism, narcissism, necrophilia,
   paraphilia, passive algolagnia, pedophilia, sadism, sadomasochism,
   sapphism, scotophilia, sexual inversion, sexual normality,
   sexual preference, swinging both ways, transvestitism, tribadism,
   tribady, voyeurism, zooerastia, zoophilia