mal·a·thi·on (m?l??-th???n?)n. An organophosphate compound, C10H19O6PS2, used as an insecticide.[Alteration (influenced by parathion) of earlier malathon : alteration of male(ate) + (me)th(yl) + -on (perhaps modeled on marathon).]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.Malathion (?mæl???a??n) n (Elements & Compounds) trademark a yellow organophosphorus insecticide used as a dust or mist for the control of house flies and garden pests. Formula: C10H19O6PS2[C20: from (diethyl) mal(eate) + thio- + -on]Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014mal?a?thi?on (?mæl ???a? ?n, -?n) n. an organic phosphate insecticide, C10H19O6S2P, of relatively low toxicity for mammals. [1953] Random House Kernerman Webster’s College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.