Find yourself writing or reading, and need to quickly find the definition of a word? The Mac makes it easy to do this using one of the following methods:
1. If you have a trackpad, move your cursor over the word and double-tap using three fingers.
2. If you don’t have a trackpad or prefer to use the keyboard, move your cursor over the word and hit Control-Command-D.
3. You can also right-click on a word and select ‘Look up’.
If you perform one of those three methods, a pop-up appears and gives the definition of the word, a Thesaurus entry, and a Wikipedia entry.
Note: This is for OS Lion 10.7+