cis (as the prefix in cisgender) is literally just the Latin term for "on this side of", opposite of trans = "on the other side of".

It's the exact same thing as heterosexual & homosexual, both from Greek, standing for hetero (from heteros) = different, and homo (from homos) = same.

Is the term "straight" also not ok, just gay people and "normal" people? And same for homosexual and "normal" people, and trans and "normal" people?