Morphologically complex words, and particularly neoclassi-cal compounds, form more than 60% of the neologisms in the biomedical field. Guessing their definitions and grouping them into semantic classes by means of lexical relations are thus two crucial improvements for handling these words, e.g., for information retrieval, indexing and text understanding applications. This paper describes a morphosemantic linguis-tic-based parser called DériF, currently developed in the framework of two projects, UMLF and VUMeF, and its appli-cation to French biomedical derived and compound words. It shows how the resulting morphologically tagged lexicon is enriched by semantic relations leading both to the synthesis of pseudo-definitions and to the constitution of classes of syno-nyms, hypo- and hypernyms