Pentyl \Pen"tyl\, n. [Penta + -yl.] (Chem.) The hypothetical radical, {C5H11}, of pentane and certain of its derivatives. Same as {Amyl}. Amyl \Am"yl\, n. [L. amylum starch + -yl. Cf. {Amidin}.] (Chem.) A hydrocarbon radical, {C5H11}, of the paraffine series found in amyl alcohol or fusel oil, etc.