| ̷ ̷ ̷ ̷ at iso- + noun
Etymology: International Scientific Vocabulary is- + butylene
: the branched-chain gaseous butylene (CH 3 ) 2 C = CH 2 obtainable from isobutane by dehydrogenation and used chiefly in making butyl rubber and gasoline components and in alkylating aromatic hydrocarbons — called also 2-methylpropene