nitrogen dioxide definition by Webster's New World
Webster's New World College Dictionary Copyright © 2010 by Wiley Publishing, Inc., Cleveland, Ohio. Used by arrangement with John Wiley & Sons, Inc.
a poisonous, reddish-brown gas, NO, used in making nitric acid, as a rocket-fuel oxidizer, etc.: it is also an air pollutant formed from automobile exhausts
nitrogen dioxide definition by American Heritage Dictionary
A poisonous brown gas, NO2, often found in smog and automobile exhaust fumes and synthesized for use as a nitrating agent, a catalyst, and an oxidizing agent.