Phen-ethyl-amine \fen-'eth-al-a-,men\ n. [phenyl fr. f. phène, fr. gk. phainein, to show (from its occurrence in illuminating gas)+ ethyl ( + yl) + amine fr. nl ammonia] 1: a naturally occurring compound found in both the animal and plant kingdoms. it is an endogenous component of the human brain. 2: any of a series of compounds containing the phenethylamine skeleton, and modified by chemical constituents at appropriate positions in the molecule.