The article analyzes the semantics and usage peculiarities of nouns basurman (obsolete, lit. ‘Muslim, unorthodox’) and varvar (‘barbarian’) in the Russian vernacular of Muscovite Rus as a reflection of the interethnic interaction of Russians and numerous ethnic groups with whom they were in contact, traded or fought. The aim of the study was to determine the place and role of these ideologemes in the picture of the world of the epoch. The material of the study was the dictionary entries for these nouns and their word-formation derivatives in the Dictionary of the Russian Vernacular of Muscovite Rus of the 16th–17th Centuries, as well as the card file data of this dictionary. The materials of Russian written monuments of the 16th and 17th centuries show that the analyzed words cannot be attributed as those denoting religion. It has been revealed that, in the discourses of acts, folklore sources, and journalism, lexemes basurman and varvar are ideologemes that mark an ‘alien’ in relation to their own people. They are syncretic words that unite a religious component and a nomination of an enemy in their meanings. During the period under study, these ideologemes converge and function in a number of contexts as synonymous. Orthodox Christians do not form an opposition exclusively with Muslims or pagan barbarians. The own vs. alien opposition involves an open series of ‘aliens’ adhering to another faith (for example, Catholicism and Lutheranism) and confronting Christians in their moral convictions, and often in military opposition. The lexeme varvar, borrowed from Greek, is usually used in the plural form, functions in written Church monuments, and has the meaning ‘an enemy of the Orthodox faith’. The kind of religion is not significant in this case: varvar refers to both a pagan and a Muslim, the key point is that matters is that this word labels a person as an ‘alien’. According to card files of the Dictionary of the Russian Vernacular of Muscovite Rus of the 16th–17th Centuries, varvar (Sg.) and varvary (Pl.) are predominantly used in the meaning of ‘Muslim, Muslims’. The religious component is the basis of the negative connotation, which motivates the usage of the lexemes basurman and varvar as obscene. In modern Russian, both ideologemes, according to the Russian National Corpus, are also used for a generalized name of an enemy, people of a different faith. However, there is a tendency of using these words for expressing a negative evaluation. As a result, the study concludes that the analyzed ideologemes are diachronic and universal. They do not disappear from the general cultural Russian code with the changing historical periods.