allylPronunciation: /ˈalʌɪl, -lɪl/Definition of allyl noun [as modifier] Chemistry of or denoting the unsaturated hydrocarbon radical CH2CHCH2:allyl alcoholDerivatives allylicPronunciation: /əˈlɪlɪk/ adjective Origin: mid 19th century: from Latin allium 'garlic' + -ylallyl in other Oxford dictionaries Definition of allyl in the US English dictionary