In this paper, we propose a knowledge discovery-based approach to ontology concept design. In our approach, concept design is a stepwise activity which exploits ontology matching techniques in order to retrieve useful external concepts semantically related to the design at hand. This way, the resulting ontology knowledge space is open towards external knowledge sources, by complementing the ontology expert knowledge with domain knowledge stored in other external sources, such as other domain ontologies, web directories, and, in general, the semantic web.