WordWeb - One-click lookup in any almost any Windows program; Hundreds of thousands of definitions and synonyms; The latest international English words; Works offline, or reference to Wikipedia and web references.
RhymeBook - RhymeBook is one of the best application that helps its users to find out the whole rhyme if they know some words of rhyme.
GoldenDict - The program has the following features: Use of WebKit for an accurate articles' representation, complete with all formatting, colors, images and links.
The Free Dictionary - The World's most comprehensive free online dictionary, thesaurus, and encyclopedia with synonyms, definitions, idioms, abbreviations, and medical, financial, legal specialized dictionaries
U-Dictionary - U-Dictionary is one of the sleekest dictionary applications, which helps in removing the language hurdles for its users and is available in 12 different languages.
Merriam-Webster - No other dictionary matches M-W's accuracy and scholarship in defining word meanings. Our pronunciation help, synonyms, usage and grammar tips set the standard.