Green’s Dictionary of Slang

1. (US drugs) a piece or ‘button’ of peyote cactus.

1982

R. De Sola Crime Dict. 83/1: legume: peyote eban or button.

2. (US campus) a lazy person, one who lies around doing nothing.

1981		Eble Campus Sl. Fall 5: legume – a tired person who feels like he or she is just vegetating.
1996		Eble Sl. and Sociability 77: In college slang, French fromage is occasioned by slang cheese objectionable; and legume translates slang vegetable.