Where does “за́падный” come from?

за́падный (Russian) comes from Russian за́пад, from Old East Slavic западъ, from Proto-Slavic *zapadъ, from Proto-Slavic pastì, from Proto-Balto-Slavic pṓˀstei, from Proto-Indo-European pēd-, from Proto-Indo-European ped- — to walk, to step; to stumble, to fall.

за́падный (Russian): Western