Where does “пословный” come from?

пословный (Russian) comes from Russian сло́во, from Old East Slavic слово, from Proto-Slavic slȍvo, from Proto-Indo-European ḱléwos, from Proto-Indo-European ḱlew-, from Proto-Indo-European ḱel- — to cover; to incline.

пословный (Russian): word-by-word, word-serial