pen·tene \ˈpen.ˌtēn\noun (-s) Etymology: International Scientific Vocabulary penta- + -ene : either of the two normal amylenes obtained from gasoline: a.: the alpha or 1-isomer CH3CH2CH2CH . CH2 — called also alpha-n-amylene, 1-pentene b.: the beta or 2-isomer CH3CH2CH . CHCH3 — called also beta-n-amylene, 2-pentene