per·mono·sulfuric acid \ˌpərˌmänō, -mō+...-\noun Etymology:per- + mon- + sulfuric : an unstable crystalline strong monobasic acid H2SO5 obtained by acid hydrolysis of persulfates or by the action of hydrogen peroxide on chlorosulfonic acid or sulfuric acid — called also Caro's acid, peroxymonosulfuric acid