The article is devoted to the study of the phenomenon of lexical-semantic interference of the English and French languages in the Middle Ages. The author indicates the relevance and significance of the research topic. A brief terminological analysis of the category «interference» is carried out, which results in the fact that at the lexical level and in the interlingual context, this phenomenon manifests itself as a result of a wide range of methods for formulating one concept in different languages, as a result of which a divergence in categories is noted. The author's interest in studying interference in the French and English languages in a diachronic aspect is due to the fact that the vocabulary of a language always reflects the history of its people. The emphasis on the problem of borrowing from French into English in the 10th–15th centuries was made due to the fact that significant historical and social events took place in the relationship between France and Britain, which could not but be reflected in the cultural and linguistic development of the latter. Focusing on the practice of language interference caused by historical and social factors, an analysis of historical events and prerequisites is carried out, as a result of which the results of the influence of the French language on English during the Middle Ages are clarified (using examples of professionalisms). Based on the results of the study and the independent selection of French equivalents for English words, the author concludes that lexical-semantic interference in this era manifested itself in the movement of similar lexical units into another language by modifying them according to the phonetic or graphic model of their language. As a rule, such a deviation from the language norm is the most frequent, since the transformation of words occurs according to the same principle as in the native language.