Definition of "cis-" []

• On this side: cisatlantic. (prefix)
• Having a pair of identical atoms or groups on the same side of a plane that passes through two carbon atoms linked by a double bond. Used of a geometric isomer: cis-2-butene. (prefix)

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.