en·do·sul·fan (?n?d?-s?l?f?n)n. A highly toxic crystalline solid, C9H6Cl6O3S, used as an insecticide and wood preservative.[endo- + sulf(o)- + -an.]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.endosulfan (??nd???s?lfæn) n (Chemistry) an insecticide used to control a variety of insectsCollins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014