Fellow masons?
Sort of, a LONG time ago.
The Masonic fraternity used to be just that, a fraternity of stone masons who passed down the secrets of stone masonry through the centuries since the building of Solomon's Temple.
As buildings became made more of wood, the craft and organization was dropping in size.
A couple of fellows where were not stone masons thought it was a good group and wanted to join, even though they weren't stone masons to help keep the organization going.
The stone masons had a conflab and decided to accept them as members.
Thus the term to describe a Mason ever since has been "free and accepted mason".
What "secrets" are there to stone masonry? And why are they secrets.
Sounds more like an agnostic labor union.