WordNet® is a large lexical database of English. Nouns, verbs, adjectives and adverbs are grouped into sets of cognitive synonyms (synsets), each expressing a distinct concept.
Clarity regarding controlled vocabularies, taxonomies, thesauri, ontologies, and metamodels. With all the scuttlebut going around about folksonomies and tagging, these are important terms to understand. In the process of tagging, it's pretty noticeable
J. Curran, and M. Moens. Proceedings of the ACL-02 workshop on Unsupervised lexical acquisition - Volume 9, page 59--66. Morristown, NJ, USA, Association for Computational Linguistics, (2002)