ENThis article deals with lexical systemic relationships between Eastern and Western regions of Lithuania. The analysis is based on the lexicon of the most important bilingual and multilingual dictionaries and religious scripts of 17–19th century. The research examines the impact of Lithuanian dialects and other languages (Latin, Polish, German) on development of lexicon. Attention is paid on neologisms (derivation models), loanwords (lexical and semantic) and dialecticisms usage and distribution of that time. Furthermore, problems of adaptation of loanwords and their integration, synonymy of lexemes and equivalence are revealed by giving certain examples of thematic lexical groups development and the formation of terminology. This paper also deals with question why some of specific words became commonly used in the standard Lithuanian but others have disappeared or remained only in Lithuanian dialects. [From the publication]