For the analysis of continuous discourse in a wide range of corpora, it is essential both to model and to expand whole-language lexical resources (e.g.,Roget’s International Thesaurus), in order to make such whole-language lexical resources adaptable to differentiated-discourse domains by means of rapid extensibility. Thus, rapidly extensible lexicons are of interest as special-domain extensions to a whole-language lexicon. My presentation argues for the validity of this approach, with specific reference to a viable conceptual, whole-language, foundational lexicon,Roget’s International Thesaurus (1962).