On this side of; on the side nearer the speaker.
[Latin cis, on this side of.]
The adjective cisalpine refers to the southern side of the Alps (from the perspective of Rome, since the Romans invented the term); cisatlantic refers to the speaker's side of the Atlantic; something cismontane is on this side of the mountain; cislunar means this side of the Moon, between the Earth and the Moon.
The form also indicates isomers of chemical compounds in which substituents at opposite ends of a carbon-carbon double bond are on the same side of the bond, as in cisplatin, an anti-tumour drug, or in formal chemical names such as cis—2—butene. Its opposite is trans-.