This paper proposes a model for describing lexical semantics within systemic-functional theory. Formal approaches to lexical semantics assume that words have meanings which exist independently from communication and are represented by means of (semi-) formal definitions. Functional approaches treat language as a tool for social interaction and, in the case of lexical semantics, assume that lexical items provide resources for realising the communicative intentions of the speaker. The paper explores problems occurring when uses of words in context are categorised according to pre-established sense distinctions and proposes a mechanism that uses systemic networks to describe meanings of lexical items as functions of their uses. The paper ends with a case study of uses of English, German and Russian verbs of motion, including options for their translation. The model is also tested empirically by considering word uses in an aligned parallel English-German-Russian corpus.