прьстень (Old Church Slavonic) comes from Proto-Slavic pьrsty, from Proto-Slavic pьrstъ, from Proto-Balto-Slavic pírštan, from Proto-Indo-European pr̥-sth₂-o-m, from Proto-Indo-European per-, from Proto-Indo-European pr̥tós — passed , crossed.
прьстень (Old Church Slavonic): ring