Ar·de·bil also Ar·da·bil (är?d?-b?l?) A city of northwest Iran near the Caspian Sea. It was probably founded in the fifth century ad.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.