First, and not as trivial as it seems: it’s a word that has a definition.
Does a word or its definition have substance?
What if it is the wrong part of speech?
For example: “a mind” may be a nominal.
But what if it is describing a verb? [called “a process” in noun form]?
If the process “of minding” is where the definition belongs, this might explain why it’s so difficult to pin it down: We’re using the wrong word form for the concept.