The paper analyses the semantic extension of a lexical unit from the vantage point of Cognitive Grammar as outlined by Langacker (1987; 1990; 2000a; 2000b; 2008, etc.). It discusses semantic extension, emphasising that it is grounded in the shared encyclopaedic knowledge and focusing on the emerging schema that the relation of extension implies. The lexical item under analysis is the French corps [body], whose extension onto the domain of musical instrument is discussed in the paper. The conclusion notes the presence of chains based on metonymic and metaphoric relations among the dimensions of complexity present in the process of semantic extension.