Idioms and compounds have similar semantic characteristics: both types of expressions are semantically composite, in the sense that their meaning is (at least in principle) composed of elementary building blocks, i.e. the constituent parts of the expressions. The present paper takes a closer look at the semantics of such composite expressions: it describes the interaction between the syntagmatic and the paradigmatic axes in the meaning of idioms and compounds, and then charts the various ways in which metaphor and metonymy can interact along these axes. Within the broad field of metaphor and metonymy research, the most direct point of comparison for the present analysis is the notion of 'metaphtonymy' introduced by Louis Goossens*. It will be argued that metaphtonymy is part of a more encompassing 'prismatic' model for the semantics of composite expressions. (Dirk Geeraerts)