The word "亚硝酸" is formed by combining three characters: 亚, meaning "sub-" and indicating a lower oxidation state in chemical terminology; 硝, derived from terms for nitrogen compounds like nitrate; and 酸, meaning acid. Together, they specify the compound nitrous acid, with 亚 modifying 硝 to denote the nitrous form, and 酸 designating it as an acid.