I would have to agree with the definition given by Master Saintans, there is definitely a big difference between the two. I am most definitely a submissive but could never be a slave.
That said, in terms of a scene, i may be termed a 'bath slave' or 'body slave'. These to me are very specific roles, which will come to an end with the scene whereas my submissiveness to my Mistress doesn't end.
jad