This article deals with the specific nature of lexicology and terminology and certain principles defining the epistemological nature of lexemes and terms. It then turns to practical concerns with a discussion of certain methodological approaches used in lexicological and terminological research, and a demonstration of practical applications. The article is structured as follows: 1. study of the principles underlying the dual reality of lexical units; 2. analysis of the linguistic origin of lexemes and terms; 3. considerations on the epistemological nature of lexemes and terms; 4. general discussion of methodological approaches in lexicology and terminology; 5. practical application.