Thesaurus - Synonyms, Antonyms, and Related Words Free Thesaurus: synonyms, antonyms, and related words. The thesaurus contains more than 145,800 unique entries from three top sources: Collins Thesaurus of the English Language - Complete and Unabridged, The American Heritage Roget''s Thesaurus, and WordNet. Search words or phrases to find synonyms, antonyms, and related words, all distinguished by color and grouped by meaning. Filter by part of speech to show only the results you want to see. Quickly find the synonyms for hundreds of thousands of words with Free Thesaurus.