From the Latin and Italian adverbial suffix -e (as in bene "well"), perhaps reinforced by the Russian adverbial -e found after a palatalized consonant.
From West Germanic *-ā, from Proto-Germanic *-ê, which survives otherwise only in Gothic (and possibly Old Norse).
From Latin -ae (“first-declension ending”)
From Proto-Slavic *-ę.
From Latin -et, the third-person singular present active indicative ending of second conjugation verbs, and Latin -it, the third-person singular present active indicative ending of third and fourth conjugation verbs.