ex·tend·er (?k-st?n?d?r)n. A substance added to another substance to modify, dilute, or add to it: meatloaf that contained oatmeal as an extender.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.extender (?k?st?nd?) n1. a person or thing that extends2. (Chemical Engineering) a substance, such as French chalk or china clay, added to paints to give them body and decrease their rate of settlement3. (Chemical Engineering) a substance added to glues and resins to dilute them or to modify their viscosity4. (Chemistry) a substance added to elastomers to assist the plasticizer5. (Printing, Lithography & Bookbinding) printing the part of certain lower-case letters that extends either above (the ascender) or below (the descender) the body of the letterCollins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014ex?tend?er (?k?st?n d?r) n. a substance added to another substance, as to paint or food, to increase its volume or bulk. [1605?15] Random House Kernerman Webster’s College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.