allyl Syllabification: (al·lyl)Pronunciation: /ˈalil/Definition of allyl noun [as modifier] Chemistry the unsaturated hydrocarbon radical CH=CHCH2:allyl alcoholDerivatives allylicPronunciation: /əˈlilik/ adjective Origin: mid 19th century: from Latin allium 'garlic' + -ylallyl in other Oxford dictionaries Definition of allyl in the British & World English dictionary