is a series of competitions in computational lexical semantics. It
started out as a competition in automatic word sense disambiguation, but
started looking a much wider variety of tasks, such as lexical
substitution (paraphrasing) and metonymy resolution. Also check out the
task list for the most recent SemEval-2010.
SIGLEX is the special interest group on lexical semantics of the Association for Computational Linguistics.
SIGSEM is the special interest group on semantics of the Association for Computational Linguistics.