noun

• (metallurgy) An industrial process for case hardening (imparting greater surface hardness to) metal objects, involving nitrocarburizing (the diffusion of carbon and nitrogen into the metal) followed by oxidation.
  "The ‘nitrox’ process basically supplies the surface hardness of the sursulf process, which is essentially carbonitriding, and then oxidizes it. The oxide is adherent and thus considerably increases the corrosion resistance."
• (underwater diving) A mixture of nitrogen and oxygen, the nitrogen content being lower than that of normal air, which is used in place of air as a breathing gas.
  ""Enriched air" or "nitrox" is a mixture of air and oxygen; the oxygen component ranges to about 50% but is used normally at 32 to 40%. [...] Safe enriched air nitrox diving practices established for the scientific diving community might be of some value and could help avoid accidents due to ignorance of its hazards and use of improper procedures."