▪ I.betaineChem.|ˈbiːteɪaɪn| [anomalously f. L. bēta beet n. + -ine4.] A chemical base (C5H11NO2) found in beet and mangold-wurzel. 1879Watts Dict.Chem. VI. 340 Betaine crystallizes in large shining hydrated crystals. ▪ II.betaine, betani obs. forms of betony.