oxidation number
Chemistry term for the hypothetical charge of an atom if all bonds were ionic. Used in redox reactions and nomenclature.
In potassium permanganate, the oxidation number of manganese is +7.
価数 (valence) is a broader concept; 酸化数 is a specific formalism used in redox chemistry.
Compound of 酸化 (oxidation) and 数 (number). A straightforward calque of the English term 'oxidation number'.