Maybe it could simply be a calque that translates the greek word. AFAIK, that would be strane for OCS.

Calque? It is not strange for OCS, acctually there is abudance of such therms. Usually, all theological concpets are translated in such way.

What is strange is that footnote cited in OP, does not refere to documents where it is usde, and obviously for some reason mistake wife and concubine.