Propionic acid (from the Greek words protos, meaning "first", and pion, meaning "fat"; also known as propanoic acid) is a naturally occurring carboxylic acid with chemical formula CH₃CH₂COOH. It is a clear liquid with a pungent and unpleasant smell somewhat resembling body odor. The anion CH₃CH₂COO^- as well as the salts and esters of propionic acid are known as propionates (or propanoates).