Dr. Dick wrote :
"'how do we come to know what words mean?' ....
The only rational answer is that "we guess"."

Surely you have not shown that "the only rational answer" is anything of the sort.
That statement is too bold.

That proposition is also simply not so, Dr. Dick. I suspect in your brilliance, you have
attempted to simplify something beyond its event horizono and reported the atomized results.

The answer is:
Words are like points on a grid or matrix.
They are defined in terms of their distance from, and difference in address in relation to, other words.
A word has zero distance from itself and by definition, no different address than itself.
That is why a word cannot be used in its own definition.
Welcome back!
Mike