perchloric acid Syllabification: (per·chlo·ric ac·id)Pronunciation: /pərˈklôrik/Definition of perchloric acid noun Chemistry a fuming toxic liquid with powerful oxidizing properties. Chemical formula: HClO4 Derivatives perchloratePronunciation: /-ˌrāt/ noun perchloric acid in other Oxford dictionaries Definition of perchloric acid in the British & World English dictionary