STRAIGHT RULER

The Latin verb regere (which could mean either "to keep straight" or "to rule") has had an enormous impact on our language. Its fourth principal part, rectus, has contributed to pretty much every word you can imagine with a rect in it: think rector (the "ruler" of a parish), direction (which originally meant "set straight")​, correct ("with straightening"), and rectum (which was considered the "straight intestine"). Then the second principle part (that being regere) developed into a bunch of words containing reg in them: this includes regime (something that rules a country), region (a piece of land historically ruled by someone), and regular (which originally meant "straight piece of wood"). Finally, there are a bunch of random descendants that underwent other changes, like dress, ergo, surge, and more.