This article is devoted to the consideration of such a phenomenon of the XXI century as hashtags - a navigation tool that helps to navigate the flow of information and redirects Internet and social network users along the path they are interested in. The purpose of this article is to study hashtags as a means of replenishing the vocabulary of modern Spanish, French and Russian languages as complex nouns of the "lexicalized sentence" type. The study was based on lexicographic, descriptive, comparative methods, as well as methods of cognitive and structural-semantic analysis and the method of continuous sampling. The features of the functioning of complex nouns of the "lexicalized sentence" type, formed from popular hashtags, are illustrated in the article with examples in Spanish, French and Russian from the modern press and the blogosphere. The scientific novelty of the study lies in the fact that hashtags are considered for the first time as a source of replenishment of the vocabulary of a particular language. A comparative analysis of the structural and semantic features of complex nouns of the "lexicalized sentence" type, formed from popular hashtags, made it possible to identify criteria for classifying such linguistic neologisms as complex nouns of this type in modern Spanish, French and Russian. The study showed that hashtags have a high functional potential and in the last two decades have been one of the productive ways to form new complex nouns such as "lexicalized sentence" in various languages.