Originally Psychology and Psychoanalysis. Sexually or romantically attracted to people of both sexes; engaging in sexual activity with both men and…

Having an ambivalent or changing sexual orientation; characterized by such sexual orientation; spec. bisexual.

Sexually or romantically attracted to people of either sex, bisexual; (also) of ambiguous sexual orientation.

practising or tolerant of both homosexual and heterosexual activity; bisexual.

Of a person: sexually attracted to both men and women; (also) of or relating to bisexual people or bisexuality; = bisexual, adj. 4a.

Both heterosexual and homosexual. slang.

slang (originally U.S.). Of a person: bisexual.