Abstract: The object of the study is the linguocultural triad mercy-indifference-cruelty in English and Russian. The subject of the study is nuclear lexemes that verbalize the linguistic and cultural concepts of mercy, indifference, cruelty in the compared languages. To reveal the essence of the concepts studied, etymological analysis of the lexemes-representatives, data from etymological dictionaries of English and Russian languages were used. The purpose of the study is to establish universal and idioethnic characteristics of the representatives of the conceptual triad mercy-indifference-cruelty in English and Russian. The following methods were used in the work carried out: semantic method, etymological method, comparative method, external reconstruction method. The scientific novelty of the work consists in the study of the linguistic and cultural concepts of mercy, indifference, cruelty in etymological perspective, which have not previously been studied in triadic relations when comparing English and Russian languages. As a result of the conducted research, we received information for the first time that nuclear lexemes verbalizing the concept of mercy in English and Russian at the initial stage of their functioning in the compared languages have similar motivation due to the presence of the first root of the Proto-Indo-European language. We have found evidence of a semantic shift in the perception of linguistic units representing the concept of indifference in English and Russian linguistic cultures in diachronic terms. A characteristic idioethnic feature of the representation of the concept of cruelty in the minds of native speakers of the Russian language is its ambiguity and dependence on casual attribution.