Propanoic acid (also known as propionic acid from the Greek words protos, meaning first, and pion, meaning fat) is a naturally occurring carboxylic acid with chemical formula CH3CH2COOH. It is a clear liquid with a pungent odor. The anion CH3CH2COO− as well as the salts and esters of propanoic acid are known as propanoates (or propionates).