Definition of caustic

• any chemical substance that burns or destroys living tissue
• harsh or corrosive in tone; "an acerbic tone piercing otherwise flowery prose"; "a barrage of acid comments"; "her acrid remarks make her many enemies"; "bitter words"; "blistering criticism"; "caustic jokes about political assassination, talk-show hosts and medical ethics"; "a sulfurous denunciation"; "a vitriolic critique"
• of a substance, especially a strong acid; capable of destroying or eating away by chemical action