This paper examines "N is N" as a nominal tautology construction, by the framework of lexico-constructional pragmatics as an emerging interdiscipline. We first demonstrate the formal (morphological, phonological and syntactic) and semantic features of the construction, and then account for the pragmatic conditions for a well-formed "N is N" construct(ion). It is maintained that the speaker, by conceptual metonymy and "pragmatic constraints", generates a grammatical metonymy underlying the second N (in the lexical/phrasal rank), and that on the basis of this he "pragma-coercively" generates a grammatical metonymy and a pragmatic metonymy (in the syntactic rank). This construction is actually a double-or even multi-metonymy matrix whose speaker, driven by high meta-pragmatic awareness, expects a given constructional effect of economy and humour apart from a given constructional meaning. On the other hand, the audience can retrieve this constructional meaning and effect only by a three-step inference that usually lasts twice or thrice.