cis-

American Heritage® Dictionary of the English Language, Fourth Edition

1. On this side: cisatlantic.
2. 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.

Wiktionary

1. On this side of, e.g. Cis-Neptunian object.
2. chemistry Forming names of chemical compounds in which two atoms or groups are situated on the same side of some plane of symmetry passing through the compound.

GNU Webster's 1913

1. A Latin preposition, sometimes used as a prefix in English words, and signifying on this side.