Abstract: Metonymy is both a tool and a result of understanding and categorizing the world.In terms of definitional structure on the intensional level, metonymy cannot be defined by means of a set of necessary and sufficient conditions.In terms of referential structure on the extensional level, the boundaries among metonymy, literal language and metaphor are not always determinate.Therefore, metonymy exhibits prototype effects.The prototype of metonymy is referential metonymy based on spatial relationship, in which vehicle and target are of whole-part relationship in the same domain, and target is more conceptually prominent than vehicle.