WordNet

WordNet is a system developed since 1985 at the Cognitive Science Laboratory at Princeton University lexical- semantic network of English.

WordNet consists of a database that contains semantic and lexical relations between words. These are designed by psycholinguistic findings, because the WordNet was originally developed to make natural language texts comprehensible for computers. The database, which is available free and freely searchable and software online is also used for other purposes.

The analog to WordNet German -speaking GermaNet is not freely available, unlike this. Open thesaurus is a similar project that is a little more modest in goals ( as a thesaurus for a word processor, only Istein relation; synonym groups are reported ), but is available under a free license.