butyric acid

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A colorless organic acid, C₄H₈O₂, occurring in animal milk fats and used in disinfectants, emulsifying agents, and pharmaceuticals.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun organic chemistry Either of the two isomeric carboxylic acids, normal butyric acid and isobutyric acid, with the chemical formula C3H7COOH, occurring in animal milk fat.
• noun organic chemistry Solely the straight chain isomer of the above, normal butyric acid or n-butyric acid, CH3(CH2)2COOH, a short chain fatty acid; its glyceride is one of the principle components of the flavour of butter.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun an unpleasant smelling fatty acid found especially in butter