Chem. designating an isomer having certain atoms or groups on the same side of a given plane in the molecule: in chemical names, usually printed in italic type and hyphenated and disregarded in alphabetization: cis-butene
< L cis, on this side: see here
See CIS in American Heritage Dictionary 4
Commonwealth of Independent States
On this side: cisatlantic.
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.
Origin: , from cis, on this side of; see ko- in Indo-European roots