OS X now contains a very helpful, pop-up dictionary. It works in textedit, safari, and terminal.

My spelling is horrible. After reading a few of my tutorials, you are probably laughing at my vocabulary as well. Apple is trying to help poor souls like me.

Highlight a word in OS X and press ctrl-cmd-D. If you are in a supported application, a dictionary will appear under the word. My own testing shows that this works in Safari, textedit, and terminal. Yes, terminal.

I do not understand why Apple did not include this helpful feature in mail and calendar. Maybe that’ll be added in the Snow Leopard version.