Book excerpt: This book describes an investigation of the subset of general language used in definition sentences and the development of a taxonomy of definition types, a grammar of definition sentences and parsing software which can extract their functional components. Based on definition sentences used in one of the dictionaries from the Cobuild range, and the book includes a brief history of the development of monolingual English dictionaries, an assessment of the concepts of sublanguages and local grammars and a full exploration of the results of the analysis and of the present and future applications of the taxonomy, grammar and parser.