The work is focused on specific underived nouns that are functioning in the Smolensk patois and in the Belarusian language at the present stage of the existence of these language systems and are quite close, but not identical formations in semantic and structural terms. The subject of the study is the volume of lexical meaning and potential derivational connections of nouns recorded in two synchronous language formations. The relevance of the study is determined by the complex history of the Russian and Belarusian borderland, which is reflected both in the Smolensk patois and in the Belarusian language, which had been created on the dialect basis. The vocabulary of the Russian and Belarusian borderland belongs to a single cultural and historical continuum de-termined by the history of the region, it reflects the diverse material and spiritual ties of the two language idioms’ speakers. The complexity of the historical relations between the two language systems, one of which is codified and has the status of an official language (Belarusian language), and the second exists only in an oral form and has a norm due to internal language laws of devel-opment (Smolensk patois), has led to the fact that when studying two language formations at the present stage, it is possible to speak not only about unambiguous types of relations between words, but also about peripheral types, about zones of various transitions, changes in lexical and grammatical semantics, which can potentially be points of development of two idioms in the future and are therefore valuable for study.