>The Late Latin adjective modernus, a derivation from the adverb modo "presently, just now", is attested from the 5th century, at first in the context of distinguishing the Christian era from the pagan era. In the 6th century, Cassiodorus appears to have been the first writer to use modernus "modern" regularly to refer to his own age.
https://en.wikipedia.org/wiki/Modernity#Etymology