The Collaborative International Dictionary of English v.0.48:

Oxidation \Ox`i*da"tion\, n. [Cf. F. oxidation.] (Chem.)
   The act or process of oxidizing, or the state or result of
   being oxidized.
   [1913 Webster]

WordNet (r) 3.0 (2006):

oxidation
    n 1: the process of oxidizing; the addition of oxygen to a
         compound with a loss of electrons; always occurs
         accompanied by reduction [syn: oxidation, oxidization,
         oxidisation]