An auto-antonym is a word that has two meanings, one the opposite of the other. 'Fearful' is an example. According to Michael Gilleland, who inspired this copy-cat post,
The Oxford English Dictionary defines fearful as both "causing fear; inspiring terror, reverence, or awe; dreadful, terrible, awful" and "frightened, timorous, timid, apprehensive."
There is much more on this topic at Dr. Gilleland's site.
There must be some philosophical terms that exhibit the auto-antonymic property. How about 'objective reality'? Suppose someone were to start talking about the objective reality of the God-idea. You would naturally take him to be raising the question whether there exists anything corresponding to this idea. But if a Descartes scholar were to speak of the objective reality (realitas objectiva) of the God-idea he would mean something nearly the opposite: he would be speaking of the representative content of the idea itself, a content that is what it is whether or not anything corresponds to the idea.