And yet we do manage to talk about it, even without a dictionary definition.
I definitely think we need to work on at least a "working" definition for our use here, which we will eventually want to add to the Lexicon and/or the FAQ. That's pretty much exactly what we have to do with "Gods" "Virtue" "Pleasure" "Truth" and probably many other words.
In this case it doesn't help much but whatever working definition probably needs to include the "not supernatural" qualifier, but obviously that's not a satisfactory start. "Divinity" is a term that presumably exists whether we recognize it or not, because "the Epicurean gods" are held to exist whether or not we know it. I presume "spirit" is also a term that is used so thoroughly that we can say that it exists whether we recognize it or not, but it's closely tied in to "mind" and "soul" and has be better articulated.
It's entirely unclear to me whether "spirit" in the Epicurean sense has any real connection with "the Epicurean gods" or what that connection would be. From the point of view of the surviving texts, we could probably have reverence for "the gods" and profit from that presumably even if we never had a "spiritual" experience.
Probably it is first necessary to define "spirit" before we define "spiritual experience." If the spirit is different from the mind, then presumably it has its own "experiences" which are different from mental or "physical" experiences. But of course there is the premise that nothing exists except "matter" and void, so whatever experiences are going on presumably have a "material" aspect to them.
I think the place to start is more the question of separating the terms "mind" "soul" and 'spirit" and determining whether they are separate entities from the Epicurean viewpoint.
NOTE: Again, I think it's best we start "from the Epicurean viewpoint" rather than "what we ourselves think is the case" because we can't really be sure whether we agree or disagree with Epicurus unless we know what HIS viewpoint was.