“Cis” is simply a latin prefix that means “on the same side of”. That is, cisgender = sex and gender are the same and have been unchanged since birth. In organic chemistry, there are cis-isomers and trans-isomers. In astronomy, the solar system contains cis-Neptunian and trans-Neptunian objects. Molecular biology describes cis-acting and trans-acting elements within DNA molecules. “Cisgender” is a useful word because it removes ambiguity, is concise, and doesn’t have any value judgement attached to it.