Disambiguate
I would think the best fit would be Disambiguate. Literally,
“to remove the ambiguity from; make unambiguous:”
I don’t think that the fact that the word is not widely used is of any relevance. In the worst case your audience will fail to understand and choose not to educate themselves as to its meaning. In the best case it communicates precisely what you intend. Unless your audience is incapable for any reason of either understanding or enlightening themselves as to the meaning of the word, it seems like a reasonable risk to take. When I hear a word I don’t know, I look it up.
