The Collaborative International Dictionary
Perchloric
Perchloric \Per*chlo"ric\, a. [Pref. per- + chloric.] (Chem.) Pertaining to, or designating, the highest oxygen acid ( HClO4), of chlorine; -- called also hyperchloric.
Wiktionary
perchloric
a. (context chemistry English) Describing compounds containing the most highly oxidized state of chlorine