The article aims to reveal the differences and the similarities of the Russian derivative preposition pod vidom [under the guise of] and its French prepositional analogue sous (le) couvert de [under the cover of], the rules of their functioning in the two languages, and to determine if they could be used as equivalents in Russian and French. The article also shows the relevance of studying prepositional derivatives as part of cognitive research. The article starts from the lexicographical analysis based on the Russian and French explanatory dictionary entries and continues with collocation analysis. Special attention is paid to the core word meaning of each prepositional locution and their collocation features in each language. It is suggested that Russian derivative preposition pod vidom and its French equivalent sous (le) couvert de could be means of representing the concept of FRAUD. The language material comprises the texts of journalistic genre collected with the help of the electronic text bases (the French newspaper archives and the Russian National Corpus); 150 context usages were found and analyzed for each of the prepositional locutions in both languages. In some bilingual dictionaries these two function words are described as translation equivalents meaning that they can be used in equal language situations in French and Russian. However, the Russian and French locutions are based on nouns with quite different meanings: the core of the Russian preposition is the noun vid [appearance, guise], the French one is formed with the help of the noun le couvert [cover]. Thus, it is presupposed that speakers could associate these two prepositional locutions with different categories. The analysis is based on the cognitive, comparative and contrastive approaches as the combination of these three approaches allows revealing the peculiarities of the usage and the shades of meanings of the two considered prepositional locutions. According to the language facts, the Russian derivative preposition pod vidom does not seem to have any collocation limits. It is used with material, concrete and abstract nouns. On the contrary, the French prepositional locution sous (le) couvert de has significant collocation restrictions: it is only compatible with abstract nouns. Furthermore, sous (le) couvert de has an additional meaning that could not be associated with the meanings its Russian analogue has and demonstrates a lower grammaticalization degree if compared with the Russian one. As a result, both similarities and differences were revealed. The two prepositional locutions form the same syntactic constructions and in some contexts have parallel meanings, but they have different inner semantics that is mostly manifested in their collocations. So, the locutions pod vidom and sous (le) couvert de cannot be presented as full equivalents in dictionaries.