1712, "sharp and bitter to the taste," formed irregularly (perhaps by influence of acrimonious) from Latin acer (fem. acris) "sharp to the senses, pungent, bitter; eager, fierce," also figuratively, of qualities, "active, ardent, spirited," also "hasty, quick, passionate;" of mind "violent, vehement; subtle, penetrating," from PIE *akri- "sharp," from root *ak- "be sharp, rise (out) to a point, pierce." Of feelings, temper, etc., in English from 1781. The -id suffix probably is in imitation of acid. Acrious (1670s) is a correct formation, but seldom seen. Related: Acridly.