I haven’t really used an offline dictionary software for my wordsmithing duties. Since I’m online almost always, I just access my browser and use Google define: operator. In any case, it provides you with a whole lot of possible definitions from different contexts.
If you’re an avid user of this Google feature, then you might want to look at this add-on too. Define: is a Firefox add-on that adds and option to your context menu to search a highlighted word using Google’s define: operator. Pretty straightforward yet very useful. Saves you the trouble of going through a few more keystrokes.
Via Firefox Facts