Protoxide /(?)/

Pro·tox·ide

Protoxide

n.
  1. That one of a series of oxides having the lowest proportion of oxygen. See Proto-, 2 (b). (Chem.)

Phrases & Compounds
protoxide of nitrogen
laughing gas, now called hyponitrous oxide<--, used as an anaesthetic in dentistry; now (1950-1996) called nitrous oxide, NO -->. See under Laughing.