This isn't directed at you, personally, but that's a common argument used by the 'Living Constitution' crowd to re-interpret and redefine the Constitution's clear meaning.
The Framers didn't define ANY of the terms they used in our founding charter. It was taken as a given by them, that the people understood and comprehended the plain meaning of English words.
It's only in our modern era that people have become so illiterate, or even purposely ignorant, that they've lost the ability to read the document and broadly agree on what it actually says.
ML/NJ