-onymysuff. A set of names; the study of a kind of names: toponymy.[Greek -?numi?, from -?numos, having a specified kind of name, from onuma, name; see n??-men- in Indo-European roots.]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.