something sensed objectively.
I think you are going in the right direction but the word "objectively" is probably a dead end. I think Epicurus is using pain and pleasure as totally subjective and we alone are the judge of it -- if it feels good, it is pleasurable, if it feels bad it is painful. If there were an "objective" standard then we would have something absolute higher than our own pain and pleasure and I think the physics / cosmology rules that out.
And oh yes, "passions" is definitely another word that needs to be considered. And yes that word has been corrupted even more so than pleasure. But passions is probably most directly related to Pathe and so part of the heritage of the words.