WordNet

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WordNet-Online free dictionary and hierarchical thesaurus of English. Definitions, synonyms, antonyms, hypernyms, hyponyms, meronyms, holonyms, derived forms and sample sentences. The handy dictionary software minimizes to your system tray and waits until you click it. You may search any English word in the dictionary and get the definition along with related words including synonyms, antonyms, particular and general concepts (e.g. Model T is a kind of car, sex is a kind of activity), parts (e.g. CPU is a part of computer), and many others. Simple install and uninstall. No spyware or adware. Try by yourself, it's fun and free!

keywords: WordNet, dictionary, thesaurus, reference, encyclopedia, hierarchical, free, ontology, definition, synonym, antonym, kind-of, part-of.
WordNet top-level concepts: entity, psychological feature, abstraction, state, event, act, human action, human activity, group, grouping, possession, phenomenon.
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