Ever look up a word in OS X’s built-in dictionary, and not know one of the words in the definition? No problem, just double-click it to get it’s definition. This doesn’t just work for some words, it works for all words. Although they don’t give you a nifty little hand cursor to indicate a link, every single word within Apple’s dictionary is double-clickable. Go ahead, try it.
As long as we’re on Dictionary tips, don’t forget that in many apps running under OS X, you can right-click (or control-click) a word and select, “Look up in Dictionary” from the contextual menu that appears. And, if you’re in Safari, you can hover your cursor over a word and hit the Command + Control + D keys to bring up a pop-up window with the definition.