Green’s Dictionary of Slang

1. a bisexual.

1968		‘Sl. of Watts’ in Current Sl. III:2 10: Bi, n. A homosexual who is capable of a heterosexual relationship.
1974		E. Wilson Show Business Laid Bare 319: ‘He’s a bi’or ‘She’s a bi’were expressions we’d heard for years about certain stars.
1993		R. Shell Iced 114: Gays, straights, bis everything and everybody.
2002		The-House-of-Love.org ‘Bisexual Names’ 🌐 ambisexual • AM/FM • bats and bowls • bi • bi-bi-baby • bi-curious • bicycle • bi-loving • bipe.

2. (Aus.) a bicep.

2010

L. Redhead Thrill City [ebook] His bi’s and tri’s were so pumped that his arms seemed [...] a little too short for his body.