tan·nin / ˈtanin/ • n. a yellowish or brownish bitter-tasting organic substance present in some galls, barks, and other plant tissues, consisting of derivatives of gallic acid, used in leather production and ink manufacture.

tannin A generic term for complex, non-nitrogenous compounds containing phenols, glycosides, or hydroxy acids, which occur widely in plants. They are toxic substances with astringent properties, whose principal function appears to be to render plant tissues unpalatable to herbivores.

tannin astringent having the property of converting hide into leather. XIX. — F. tanin, f. tan TAN + -in -IN.
So tannic XIX. — F. tannique.

tannin One of a group of complex organic chemicals commonly found in leaves, unripe fruits, and the bark of trees. Their function is uncertain: the unpleasant taste may discourage grazing animals, or they may help form barriers against the entry of pathogens. Some tannins have commercial uses, notably in the production of leather and ink.

tannin A generic term for complex, non-nitrogenous compounds containing phenols, glycosides, or hydroxy acids, which occur widely in plants. They are toxic substances with astringent properties, whose principal function appears to be to render plant tissues unpalatable to herbivores.