gallic acidEnglishOxford Dictionary of Englishgallic acid /ˈɡalɪk / ▸ noun [mass noun] Chemistry an acid extracted from oak galls and other vegetable products, formerly used in making ink. Alternative name: 3,4,5-trihydroxybenzoic acid; chemical formula: C6H2(OH)3COOH. – ORIGIN late 18th century: gallic from Latin galla ‘oak gall’ (see gall3) + -ic.