fulminic acidPronunciation: /fʌlˈmɪnɪk, fʊl-/Definition of fulminic acid noun [mass noun] Chemistry a very unstable acid isomeric with cyanic acid. Chemical formula: HONC Origin: early 19th century: fulminic from Latin fulmen, fulmin- 'lightning' + -icfulminic acid in other Oxford dictionaries Definition of fulminic acid in the US English dictionary