In my bottom vs. submissive post, Uxorious Mate asked about my definition of a submissive.
I don't plan to write anything long here... but I do wish it to be asterisk free, without the need for special cases, conditionals, additional terms, or things of that nature.
On its most basic level, I believe a submissive is someone that willingly accepts a recognized role of inferior status in a personal relationship. Inversely, I believe on its most basic level that a Dominant is someone that willingly accepts a recognized role of superior status in a personal relationship.
I hope this is enough to work from. I think this tends to cover most specialized relationship types as well as separates it from non-consensual abusive relationships as well.