WordNet® is an online lexical reference system whose design is inspired by current psycholinguistic theories of human lexical memory. English nouns, verbs, adjectives and adverbs are organized into synonym sets, each representing one underlying lexical concept. Different relations link the synonym sets.
M. McHale. Proceedings of the COLING/ACL Workshop on Usage of WordNet in Natural Language Processing Systems, August 16, 1998, Montreal, Canada, Association for Computational Linguistics, Morristown, NJ, USA, (1998)