The word 'supernatural' is ill-defined: if something exists in the real world, then it is natural by definition.

Yeah, just like the word 'metaphysics' is ill-defined. If something exists in the real world, then it is physical by definition.

Or to be even more snarky but at least more explanatory: I doubt that 'exists', 'physical', 'meta-', 'super-' or 'natural' are sufficiently well-defined in these contexts for your accusation of ill-definition to hold any weight. If I try to interpret what you're saying in roughly the same manner in which it seems to me that you're interpreting what most folk mean by 'supernatural', except instead of being uncharitable in the direction of being snobbishly literal I reverse it and be uncharitable in the direction of not paying attention to your explicit message, it looks something like this: "People who use the word 'supernatural' tend to be wrong in obvious ways and I like to point this out in a mildly intellectual fashion so that I can feel superior to them; also since I just denounced the enemy tribe you should like me more". But that would be no more accurate a characterization of what you meant, than your characterization of what is typically meant by 'supernatural', and nobody on either side would learn anything from such analysis.

(This comment is not really a reply to User:bogus so much as an expression of annoyance at certain traditional rationalist memes. Sorry you got caught in the crossfire, User:bogus.)

What's a "supernatural entity"?

The naive impression of "mind" in general philosophical discussion is a good example of a supernatural entity -- the concept of mind separated from a specific human brain, some almost spirit-like entity.

In order to commit the mind-projection fallacy, you have to forget (really: not notice) that your brain actually exists and is not an objective observer of fact, but only an opinion-generating machine. Thus, discussions of consciousness and "qualia" are hugely hampered by forgetting that the mind is not an abstraction, it's a specific physical thing, and that the various properties being attributed to it in these discussions exist only in the brain of the beholder, rather than in the thing being discussed. (As a natural consequence of physics not having layers or levels.)

The word 'supernatural' is ill-defined: if something exists in the real world, then it is natural by definition.

Exactly.