nitrous oxiden. A colorless, sweet-tasting gas, N2O, used as a mild anesthetic in dentistry and surgery.American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.nitrous oxide n (Elements & Compounds) a colourless nonflammable slightly soluble gas with a sweet smell: used as an anaesthetic in dentistry and surgery. Formula: N2O. Systematic name: dinitrogen oxide Also called: laughing gas Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014ni?trous ox?ide n. a colorless, sweet-smelling gas, N2O, that may induce euphoria when inhaled: used for mild anesthesia. [1790?1800] Random House Kernerman Webster’s College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.nitrous oxide A colorless, sweet-smelling gas, N2O. It is used as a mild anesthetic, in which use it is often called laughing gas. Nitrous oxide occurs naturally in the atmosphere and is a greenhouse gas.The American Heritage® Student Science Dictionary, Second Edition. Copyright © 2014 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.