I like to point to 2 theories that still exist (at least in the language of the day...)
1. The /Theory/ of Evolution - this one is a common cite and still has not been proven for lack of a “link” from primate to human.
2. The Pythagorean /Theorem/ - this one is more fun for “gigging” scientists. It remains a theorem because not all value combinations have been tried. Yet it always works every time you try it.