hmm well to me Dominant is a general term, encompassing a large group of people.
i'm not really sure i've set myself a definition for "Mentor", though i guess i sort of imagine it as someone who would want to teach a submissive about the lifestyle without actively engaging in lifestyle activies with said submissive.
And Master to me is a title chosen by either a Dom or his sub as an indication of respect. To me a Master owns a submissive, rather than just knowing that he is Dominant... And i also really belive it is simply a preference thing. i've spoken to Doms who simply want to be addressed as Dom, where as others have a large preference toward Master or some other title.