tannic acid

  1. a yellowish, astringent substance, CHO, derived from oak bark, gallnuts, etc. and used in tanning hides, in medicine, etc.
  2. any of a number of similar substances

See tannic acid in American Heritage Dictionary 4

noun
  1. A white or yellowish astringent powder, C14H10O9, derived from nutgalls and used as a denaturant and in tanning and textiles.
  2. A lustrous yellowish to light brown amorphous, powdered, flaked, or spongy mass having the approximate composition C76H52O46, derived from the bark and fruit of many plants and used in photography, as a mordant, and to clarify wine and beer.

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