Consult the Dictionary trick in osX for Safari and Mail

One of my favorite little secrets in Tiger is the Dictionary/Thesaurus pop-up window that appears in applications such as Safari and Mail. Simply hover your cursor over any word and press apple-control-D to bring up a small window with the word’s definition. If you keep the control and Command keys pressed, you can then mouse over other words to see their dictionary or thesaurus entries as well. You can even highlight just part of a word (embark from disembarkation, for instance) to get the definition of a word within a word, or a part of a compound word (such as science from science fiction)