Wordnets have been created in many languages, revealing both their lexical commonalities and diversity. The next challenge is to make multilingual wordnets fully interoperable. The EuroWordNet experience revealed the shortcomings of an interlingua based on a natural language. Instead, we propose a model based on the division of the lexicon and a language-independent, formal ontology that serves as the hub interlinking the language-specific lexicons. The ontology avoids the idiosyncracies of the lexicon and furthermore allows formal reasoning about the concepts it contains. We address the division of labor between ontology and lexicon. Finally, we illustrate our model in the context of a domain-specific multilingual information system based on a central ontology and interconnected wordnets in seven languages.