Dictionary.net

• the degree of oxidation of an atom or ion or molecule; for simple atoms or ions the oxidation number is equal to the ionic charge; "the oxidation number of hydrogen is +1 and of oxygen is -2"

2006 - WordNet 3.0
By Princeton University

• the degree of oxidation of an atom or ion or molecule; for simple atoms or ions the oxidation number is equal to the ionic charge; "the oxidation number of hydrogen is +1 and of oxygen is -2"

2011 - English Dictionary Database
By DataStellar Co., Ltd