Abstract In this chapter we propose to treat metonymy as a cognitive operation of conceptual elaboration based on the part-whole relationship that is triggered by the use of an expression (or metonymic vehicle) associated with a certain conceptual cluster (or metonymic source) within a conceptual domain. The activation of the source conceptual cluster opens up a mental space which is dynamically expanded or reduced, in the sense of Ruiz de Mendoza (1999, 2000), so as to come as close as possible to fitting the conceptual givens provided by the co(n)text of use. By approaching metonymy in this manner we are able to explain in a very natural way a number of facts observed in recent research.