Any one of a group of complex nonuniform plant constituents that can be classified into hydrolyzable tannins (esters of a sugar, usually glucose, and one or several trihydroxybenzenecarboxylic acids) and condensed tannins (derivatives of flavonols). Tannins are used in tanning, dyeing, photography, and as clarifying agents for beer and wine. Sometimes used synonymously with tannic acid. Tannins form black stains in the presence of iron.
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Examples: glitazone, GI cocktail, etc.