примо́рье (Russian) comes from Russian мо́ре, from Old East Slavic море, from Proto-Slavic moře, from Proto-Balto-Slavic *mári, from Proto-Indo-European móri, from Proto-Indo-European mer- — to die; to disappear; sea, lake, wetland.
Ancestry of “примо́рье”, step by step
примо́рье traces back through two separate lines of ancestry.