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Ignition of a substance, such as oily rags or hay, caused by a localized heat-increasing reaction between the oxidant and the fuel and not involving addition of heat from an outside source.
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.
(Chemistry) the ignition of a substance or body as a result of internal oxidation processes, without the application of an external source of heat, occurring in finely powdered ores, coal, straw, etc
Collins English Dictionary – Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014
the ignition of a substance or body without heat from any external source.
Random House Kernerman Webster's College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.
The bursting into flame of a mass of material as a result of chemical reactions within the substance, without the addition of heat from an external source. Oily rags and damp hay, for example, are subject to spontaneous combustion.
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.