A definition can be seen as a central working tool for researchers, since it leads to a new conceptual construction. At the same time a multitude of definitions, especially if competing with each other, is quite often perceived as a typical symptom of fields of research that have not yet developed their theories to the necessary level of sophistication. A relatively young field of research, Translation Studies and its proponents have repeatedly been the target of criticism in that respect, i.e. working with concepts whose definitions do not comply with commonly accepted standards of definition. That kind of critique serves as the starting point for this paper, which tries to analyze definitions in two seminal publications in the history of German Übersetzungswissenschaft, representing two opposing approaches to translation, namely Zufall und Gesetzmäßigkeit in der Übersetzung by Otto Kade (1968) and Grundlegung einer allgemeinen Translationstheorie by Hans J. Vermeer and Katharina Reiß (1984). The paper gives an account of standards of definition, commonly found in philosophy of science and terminology, addresses central aspects of scientific concepts (theory-boundness, types of concepts, determinacy, vagueness) and present the findings of a study focusing on defining patterns.