Clay·ton (kl?t?n), John Middleton 1796-1856. American public official who as secretary of state (1849-1850) negotiated the Clayton-Bulwer Treaty with Great Britain (1850), establishing the neutrality of a proposed canal across Central America.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.