fumarylChem.|ˈfjuːmərɪl, -aɪl| [f. fumaric a. + -yl.] = fumaroyl. 1864Watts Dict.Chem. II. 747 Chloride of Fumaryl.1963Jrnl.Pharmaceut.Sci. LII. 1168 There are marked differences in biological potency between maleyl and fumaryl dicholines compared with succinyl dicholine.