Free online dictionaries are incomplete; print dictionaries are allll the way over there. For great instant reference when you're online, try the Oxford English Dictionary's "Search OED Online" widget.
Drag the app to your browser toolbar. After that, highlight any word on a web page, click the button on your toolbar, and you'll see the OED definition. See not only the meaning of the word, but its earliest use and usage through time. Endless fun for bibliophiles and word freaks.
The widget connects to Norlin's OED subscription, so it works on campus or from home if you're signed in through VPN.