(chemistry) An antibacterial agent obtained from lichens of the genus Usnea.

(biochemistry) a bicyclic heterocyclic phenolic compound, formed in the body by the metabolism of protein and excreted in the urine (or in faeces, as in birds and insects)

(chemistry) A short chain aliphatic carboxylic acid, CH₃(CH₂)₃COOH, obtained from the roots of valerian; used in perfume, flavourings, pharmaceuticals

Rain which is unusually acidic (pH of less than the natural range of 5 to 6); caused mainly by atmospheric pollution with sulphur dioxide, carbon dioxide and nitrogen compounds.

(chemistry) a class of strong organic acids, only known as their salts in which the negative charge is stabilized by resonance.

(biochemistry) A naturally occurring organic compound, 3,4,5-Trihydroxy-1-cyclohexene-1-carboxylic Acid, extracted commercially from star anise; it is the base of very many natural products and is used in the production of the antiviral drug Tamiflu.

(chemistry) dihydroxycinnamic acid, obtained from certain umbelliferous plants

(chemistry) a complex mixture of organic acids produced by the decomposition of vegetable matter

a red, crystalline dye, of uncertain composition, obtained from sandalwood

(organic chemistry) a carboxylic acid that also contains a hydroxy group