sialic acid Syllabification: (si·al·ic ac·id)Pronunciation: /sīˈalik/Definition of sialic acid noun Biochemistry a substance present in saliva that consists of acyl derivatives of neuraminic acid. Origin: 1950s: sialic from Greek sialon 'saliva' + -icsialic acid in other Oxford dictionaries Definition of sialic acid in the British & World English dictionary