noun
: any of several oxides of nitrogen some of which are formed in a mixture as toxic fumes by the action of nitric acid on oxidizable material (as organic substances or metals) or by the decomposition of nitrates or nitro compounds and are used as catalysts in the chamber process of making sulfuric acid: as
a. : nitrous oxide
b. : nitric oxide
c. : nitrogen trioxide
d. : nitrogen dioxide
e. : nitrogen pentoxide