The Collaborative International Dictionary of English v.0.48:
Propyl \Pro"pyl\, n. [Propionic + -yl.] (Chem.) The hypothetical radical C3H7, regarded as the essential residue of propane and related compounds. [1913 Webster]WordNet (r) 3.0 (2006):
propyl n 1: the monovalent organic group C3H7- obtained from propane [syn: propyl, propyl group, propyl radical]