per mensem

[ per men-sem; English per men-suh m ]
/ pɛr ˈmɛn sɛm; English pər ˈmɛn səm /

adverb Latin.

by the month.

British Dictionary definitions for per mensem

per mensem
/ Latin (ˈpɜː ˈmɛnsəm) /

adverb

every month or by the month