WordNet-Online dictionary 

WordNet-Online free dictionary and hierarchical thesaurus of English. Definitions, synonyms, antonyms, hypernyms, hyponyms, meronyms, holonyms, derived forms and sample sentences.
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WordWeb 

WordWeb is a powerful free English thesaurus and dictionary. Find definitions and synonyms, as well as various sets of related words. The database has over 150 000 root words. The program can be used on its own or with almost any Windows program.
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SpellExpress(tm) -- Instant Spell-Check, Thesaurus & Dictionary 

SpellExpress provides instant access to a spell-check and thesaurus directly from your desktop. With SpellExpress you can spell-check a word or phrase and find meanings, synonyms, and antonyms from any application.
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Addict 

Addict is a professional component suite that provides end-to-end solutions for adding spelling check and thesaurus support to your applications.
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Write Source 

Write and modify your text with a complete suite of applications: EditExt, ExactWord, Word Spring (spell check, Thesaurus & Definitions). Improved Compatibility Mode enhances spell checking Microsoft Word, Internet Explorer, Outlook Express and more.
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Special English Dutch Palm 

Dictionary English/Dutch & Dutch/English (over 600,000 entries). Thesaurus English (280,000 entries) and Thesaurus Dutch (180,000 entries). Conjugation English (500,000 conjugated forms) and Conjugation Dutch (600,000 conjugated forms).
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