hydrochloric acid Syllabification: (hy·dro·chlo·ric ac·id)Pronunciation: /ˌhīdrəˈklôrik/Translate hydrochloric acid | into German | into Italian Definition of hydrochloric acid noun Chemistry a strongly acidic solution of the gas hydrogen chloride in water. Chemical formula: HCl hydrochloric acid in other Oxford dictionaries Definition of hydrochloric acid in the British & World English dictionary