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Webster 1913 Edition

Noun.

[

Proto-

oxide

: cf. F.

protoxide

(Chem.)

That one of a series of oxides having the lowest proportion of oxygen. See

, 2

(b)

protoxide of nitrogen

laughing gas, now called

hyponitrous oxide

. See under

protoxide ‎(plural protoxides)

(obsolete, chemistry) the oxide of a particular element (that has multiple oxides) having the smallest proportion of oxygen