Real Dictionary

nitrogen dioxide in American English
a poisonous, reddish-brown gas, NO2, used in making nitric acid, as a rocket-fuel oxidizer, etc.: it is also an air pollutant formed from automobile exhausts
noun: a reddish-brown, highly poisonous gas, NO2, used as an intermediate in the manufacture of nitric and sulfuric acids, and as a nitrating and oxidizing agent; a major air pollutant from the exhaust of internal combustion engines that are not fitted with pol

nitrogen dioxide in British English
noun: a red-brown poisonous irritating gas that, at ordinary temperatures, exists in equilibrium with dinitrogen tetroxide. It is an intermediate in the manufacture of nitric acid, a nitrating agent, and also an oxidizer for rocket fuels. Formula: NO2