Artha

Artha is a free open-source thesaurus with WordNet as its database.

The main focus of Artha is high usuability, with much simplicity. It

has distinct features like hot key combo lookup, notifications, regex

search, spelling suggestions, etc. Once the application is launched,

it sits on the system tray. The user can select text on any window, and

call Artha by pressing the set hot key combination, which pops up Artha

with the word looked-up. If the user wants notifications, rather than

the app. popping up, it can be done by enabling notifications, which

results in a (balloon tip) notification of the selected word's prime

definition from WordNet, from the system tray, when the hot hey is

pressed.