'Tannin' definitions:

Definition of 'tannin'

noun

Any of various complex phenolic substances of plant origin; used in tanning and in medicine [syn: tannin, tannic acid]

From: GCIDE

Tannin \Tan"nin\, n. [Cf. F. tannin.] (Chem.) Same as Tannic acid, under Tannic. [1913 Webster]

From: GCIDE

Tannic \Tan"nic\, a. Of or pertaining to tan; derived from, or resembling, tan; as, tannic acid. [1913 Webster]
Tannic acid. (Chem.) (a) An acid obtained from nutgalls as a yellow amorphous substance, C14H10O9, having an astringent taste, and forming with ferric salts a bluish-black compound, which is the basis of common ink. Called also tannin, and gallotannic acid. (b) By extension, any one of a series of astringent substances resembling tannin proper, widely diffused through the vegetable kingdom, as in oak bark, willow, catechu, tea, coffee, etc. [1913 Webster]