- a yellowish, astringent substance, CHO, derived from oak bark, gallnuts, etc. and used in tanning hides, in medicine, etc.
- any of a number of similar substances
- A hydrolyzable tannin in the form of a lustrous yellowish to light brown amorphous, powdered, flaked, or spongy substance having the approximate composition C76H52O46, derived from certain plants and used in tanning leather, in fixing dyes to materials, and in clarifying wine and beer.
- See tannin.