Pertaining to, derived from, or designating, an organic acid which is produced in the distillation of wood, in the fermentation of various organic substances, as glycerin, calcium lactate, etc., and is obtained as a colorless liquid having a sharp, pungent odor. Propionic acid is so called because it is the first or lowest member of the fatty acid series whose salts have a fatty feel.  [1913 Webster]