methyl UK /ˈmɛθaɪl/US /ˈmɛθəl/ noun1 •The univalent hydrocarbon radical, CH₃-, formally derived from methane by the loss of a hydrogen atom; a compound or part of a compound formed by the attachment of such a radical.The southern acetates must be decarboxylated to methyls. — 2003 formsmethyls