The article addresses the problematics of the use of the qualitative adjective corteis in the Old French epic poems of the 12-13 ^th centuries included in “Le petit cycle de Guillaume d'Orange”. This adjective characterizes its object as belonging to the royal court and implies a whole series of notions important for medieval consciousness. On the basis of this adjective, an abstract noun courtoisie is formed in the middle of the 12 ^th century, which stands among the most important concepts of medieval culture. Its peculiarity is that in texts it can syncretically implement several meanings, becoming almost eurysemantic. Despite the fact that the issue of polysemy/eurysemy/syncretism has been covered in detail on the example of modern languages, the lack of research in terms of historical perspective determines the relevance of this study. Besides, the adjective corteis has not yet been examined by scholars from this angle. The authors of this article discovered that depending on animate/inanimate nature of the object, gender and social status of character, corteis syncretically implemented several meanings: “corresponding to court etiquette”, “glorious”; “brave”, “generous”, “polite”, “wise”; “noble”, “well-bred”, “beautiful”. In other words, corteis was syncretic both out of context and in texts. The methods of contextual and etymological analysis as well as elements of concept analysis as in works by Iu. Stepanov and V. Kolesov were used in the study.