| Noun | 1. | mescaline - the hallucinatory alkaloid that is the active agent in mescal buttonshallucinogen, hallucinogenic drug, psychedelic drug, psychodelic drug - a psychoactive drug that induces hallucinations or altered sensory experiences magic mushroom, mescal button, sacred mushroom - the button-shaped top of the mescal cactus; a source of psilocybin |