WordWeb Pro can look up words in virtually any program with just one click
just hold down the Ctrl key and right-click on the word. If you are online
with one extra click you can also search web references, for example Wikipedia
The hotkey can be customized, or you can use a keyboard shortcut if you prefer.

If you are editing a document you can select a synonym and replace the look-up
word. WordWeb has the option to highlight widely used synonyms, great for helping
you write clear easy-to-understand English.

Features:

    Exploring senses
    Web references
    Use custom glossaries
    Find words
    Full-text definition search
    Anagrams
    Add definitions
    Learn vocabulary
    Replace, copy and paste
    Proper Nouns