butyl /byo̅o̅″til/ [Gk, boutyron, butter, hyle, matter] , a hydrocarbon radical (C4H9), most compounds of which are obtained from petroleum. It exists as four isomers: n-butyl, isobutyl, secondary butyl, and tertiary butyl. Butyl compounds, some of which are toxic and irritating, are used in a variety of industrial and medical applications, including anesthesia.
