noun
: either of two isomeric fatty acids C 3 H 7 COOH:
a. : the normal acid CH 3 CH 2 CH 2 COOH found especially in butter in the form of glycerides and in rancid butter as the free acid, obtained as a colorless liquid of unpleasant odor usually by oxidation of normal butyl alcohol or butyraldehyde or by fermentation (as of molasses), and used chiefly in making esters (as simple esters for use as flavoring materials or esters of cellulose for use as plastics) — called also butanoic acid, n-butyric acid
b. : isobutyric acid