The subject of research in this paper are the adverbial and semi-adverbial phrases (with incomplete lexicalization), which derive from the adhesion of preposition to a full-sense word in the medieval Bulgarian language. The empirical material is systematized on the basis of the preposition involved in the word formation, in view of the adjunct determined by the newlyformed adverbs and on the basis of the lexico-grammatical affiliation of the motivating word.