n. [ From Olefiant. ] 1. (Chem.) Olefiant gas, or ethylene. See Ethylene. [ archaic ] [ 1913 Webster ]

2. Hence: (Chem.) Any one of the series of unsaturated hydrocarbons of which ethylene is the type; a member of the alkene series of hydrocarbons; an alkene. [ 1913 Webster + PJC ]