Pro*tox"ide (?), n. [Proto- + oxide: cf. F. protoxide.] Chem.
That one of a series of oxides having the lowest proportion of oxygen. See Proto-, 2 (b).
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.
© Webster 1913.