WordWeb is a comprehensive dictionary and thesaurus application for English language learners of all levels. It provides a comprehensive reference for English words, including definitions, synonyms, antonyms, and related words. WordWeb also includes a variety of other reference tools such as audio pronunciations, inflected forms, and usage examples. The application is available both as a desktop program and as a web-based service. It can be used to quickly look up words, get detailed definitions, and explore related words and concepts. This makes WordWeb an invaluable reference tool for English learners, as well as a great resource for ESL teachers.
Discontinued The program is no longer updated. The latest version, v2.9.2, released in August 2014, can still be downloaded from the official website.
Instant pop-up service, external and user-defined dictionaries make it better.
It is a proper dictionary. Open source. You can even use the same dictionary that Word Web uses. You can also use the more comprehensive Wiktionary if you so choose.
Dictionary.com
Artha
Lingoes
Aard Dictionary
Gnome Dictionary
TheSage
Power Thesaurus
TemaTres
QwickUp
Thesaurus.com
Treegle: Dictionary
Eko
TopWordsLike.com
It is good best for fast search of a meaning of a word. Almost like the world wide web.