WordWeb

WordWeb and it is a stand-alone dictionary
and thesaurus. The program sits in the System Tray and you can
call it up from just about any program you may be using including
your browser. To check a word, you simply highlight it and click
the tray icon or use a keyboard shortcut. The WordWeb dialog
appears and presents you with a definition of the word as well as
a list of synonyms. If the word is spelled incorrectly, it will
present an alternative where possible as well as a list of like
words for you to choose from. You can substitute the word with
one from the list by using the "replace" button.

You can also enter a word directly into the search field and have
the search function present you with a definition, synonyms,
antonyms and more.

This software is excellent if you are working in text editors,
email clients, html editors or other programs that might not have
access to the powerful grammar and spelling functionality of
software like MS Word. It also very handy for checking the
meanings of words you may encounter while browsing the Internet.

The program is compatible with Win 95, 98, NT, 2000 and XP.

You can find out more about the program from the following links:
Developer's Website
Download Mirror

NOTE: This version of the program is freeware and fully
functional. However, there is a Pro version of the software that
offers extra options for a fee.