This article discusses the issue of studying outdated vocabulary of the Russian language. The reasons for the occurrence of this process are indicated and examples are given. It is noted that the process of emergence of lexical dearhaization is studied using a historical approach. As an example, the classification of Russian linguist N.M. is given. Shansky. In his classification N.M. Shansky, considering obsolete words, divides them into three groups: words that have completely disappeared; ancient words found as root elements of modern words and words included in stable phraseological units.