This paper addresses the design of an Onomasiological Search System, a concept-oriented tool to find terms from a user description of a concept. Two conditions concerned with the application in a terminological domain and the language of application are initially stipulated in the design of the OSS to enable their implementation. The principles of the system, the architecture and its components, are presented as part of the design. This also includes an idealised user interface, with a discussion of the organisation of the probable terms and additional information that can help the user to identify precisely the term he is looking for.