We propose in this paper a formalization of the BDef lexicographic definitions pro- posed by (Altman et Polguere, 2003), in order to carry calculus on them. The information richness of such definitions suggest many calculus that are useful for lexicographic practice as well as for a more general reflection on modelling lexical semantics. Such calculus cannot be realized without a thorough formalization of such definitions that we propose to represent as typed feature structures (Carpenter, 1992). The formalization proposed allow to automati- cally check for the lexicon consistency, which suggest a new methodology for lexical description based on successive enrichment of the lexical database and the meta data that describe it. MOTS-CLES: definitions lexicographiques formalisees, regles lexicales, structures de traits typees, calculs lies aux descriptions lexicales.