1. Oxidation, a reaction in which the atoms of an element lose electrons. (wiktionary.org)
2. The act or process of oxidizing. (merriam-webster.com)
3. The state or result of being oxidized. (merriam-webster.com)
4. The process of oxidizing; the addition of oxygen to a compound with a loss of electrons; always occurs accompanied by reduction. (wordnetweb.princeton.edu)
Word origin: Noun of action from oxider “oxidize,” from oxide, coined by G. de Morveau and A. Lavoisier from ox(ygène).