I am asking after answering on the ELU.SE sent me on a expedition through the internet. The originating question asked about the meaning of the word proper after the word cell.
At first I was certain about it being a biology term describing some sort of cell. I am not a biologist. After some pushback I researched a bit and found what seems to be the original definition in a book from 1853. Link.
My question now is if you would consider cell proper a biology term or concept that is understood by an expert of cellular structures?