The potential of knowledge-based technological support for work in the legal domain has become widely recognized in recent time. This paper argues for an approach that is meant to complement existing work on top-level, statute-based ontologies for the law by extracting conceptual knowledge from verdict texts. Starting from a corpus-based survey on the definition and modification of concepts in German court verdicts we are currently working out a detailed description of the linguistic structures and semantic mechanisms involved. Based on this we want to develop tools that automatically recognize and process portions of verdicts that contain definitions. The resulting system will support the corpusbased extension of (hand-made) top-level legal ontologies and the update of legal terminological knowledge bases with regard to new jurisdiction. The research described in the paper is conducted at the Saarbrücken computational linguistics (CL) group within the project CORTE (computational linguistic methods for legal terminology).