Thom·sen (t?m?s?n), Christian Jürgensen 1788-1865. Danish archaeologist who proposed a three-part system for the chronological classification of prehistoric artifacts, divided into the Stone, Bronze, and Iron Ages. See Usage Note at Three Age system.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.