1. Biochem.a compound, C5H4N4O3, present in mammalian urine in small amounts, and the principal nitrogenous component of the excrement of reptiles and birds, that in the form of its salts occurs in the joints in gout and as the major constituent of kidney stones.
2. Chem.a white, crystalline, odorless, tasteless, very slightly water-soluble powder form of this compound, obtained chiefly from urine or bird excrement or synthesized, used chiefly in organic synthesis.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.