chlorous acid
Technical term in chemistry; refers to the inorganic acid HClO₂.
Chlorous acid is unstable and exists only in aqueous solution.
Compound of 亜 (a-, 'sub-') + 塩素 (enso, 'chlorine') + 酸 (san, 'acid'). The prefix 亜 indicates a lower oxidation state compared to 塩素酸.