Catechin \Cat"e*chin\, n. (Chem.) One of the tannic acids ({C15H14O6}), extracted from {catechu} as a white, crystalline substance; -- called also {catechuic acid}, {catechinic acid}, {cyanidol}, and {catechuin}. It is a flavonoid found generally in higher woody plants, and is used in dyeing and tanning. [1913 Webster +PJC]