Synonymy in the majority of cases is represented by derivative words. The derivative synonyms are proposed to explore by means of semantic transformation of the derivation square - the synonymous square. Such squares differ in characteristic obligatory and optional criteria, and depending on reproduction of synonymic relations of producing words by derivatives they are divided into reflected and quasi-reflected ones.

Reflection is regarded as a lexical and word-formative phenomenon. Derivative homonyms, polysemantemes, synonyms, antonyms, conversions isomorphically or homomorphically reproduce structural and semantic characteristics of derivative units, duplicating, as if reflecting them in their own semantic structures. As a result reflection becomes a strong factor of orderliness and systematization of lexicon.