cis- prefix Etymology: Latin, from cis — more at he 1.: on this side : on the nearer side — often joined to second element with a hyphen < cisalpine > < cis-Alleghany > — compare trans-, ultra- 2.: nearer in time : since < cisatomic > 3.usually italic: cis < cis-dichloro-ethylene > — opposed to trans-; see cis-trans isomerism