The Collaborative International Dictionary
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.
Wiktionary
n. (context organic compound English) catechol
Wikipedia
Catechin is a flavan-3-ol, a type of natural phenol and antioxidant. It is a plant secondary metabolite. It belongs to the group of flavan-3-ols (or simply flavanols), part of the chemical family of flavonoids.
The name of the catechin chemical family derives from catechu, which is the tannic juice or boiled extract of Mimosa catechu ( Acacia catechu L.f).