WordNet is a large lexical database of English, developed under
the direction of George A. Miller. Nouns, verbs, adjectives and
adverbs are grouped into sets of cognitive synonyms (synsets), each
expressing a distinct concept. Synsets are interlinked by means of
conceptual-semantic and lexical relations. The resulting network
of meaningfully related words and concepts can be navigated with
the browser. WordNet is also freely and publicly available for
download. WordNet's structure makes it a useful tool for computational
linguistics and natural language processing.

Homepage:
https://wordnet.princeton.edu/
