(carboxylic acid) The simplest carboxylic acid, HCOOH, a colourless, corrosive liquid with a sharp odour systematically known as methanoic acid; it is present in the stings of ants, bees and nettles, and is prepared industrially by the oxidation of methanol or formaldehyde; it has some industrial uses, and its esters, the formates are used in perfumes.