1In the names of substances containing two allyl groups.
2 rare A liquid diene (hydrocarbon) containing two double bonds, whose molecule is equivalent to two allyl groups combined.
Systematic name: hexa-1,5-diene; CH₂:CHCH₂CH₂CH:CH₂.
Mid 19th century; earliest use found in William A. Miller (1817–1870), chemist. From di- + allyl.