If you are like me who uses Leopard’s built-in dictionary very often, you probably wish / want to assign a keyboard shortcut to the “Look Up in Dictionary” service; by pressing key combination, you will be able to look up a word in dictionary instantly…instead of having to copy the word and paste it in the dictionary yourself. (you can also paste the word in Spotlight, or drag and drop the word onto the dictionary app icon in the dock if you have one…) Although not all apps (apps = applications; E.g. iTunes, Word, Photoshop etc.) support the “Look Up in Dictionary” service, its still quite useful if you use Preview to read PDF books / lecture notes; or use Safari as your web browser. Well, it turns out that by default, Apple do have a default keyboard shortcut for the service, but the name wasn’t quite right…. Just in case you are lost…here is where you can find the “Look Up in Dictionary” service:
As you can see, there is no keyboard shortcut set for the service….but wait…lets have a look at the picture below:
If you look closely, you will see that instead of “Look Up in Dictionary“, they use “Look up in Dictionary” instead! At the moment, I am using 10.5.3, and this tiny little “bug” is still not fixed…maybe in the previous builds (10.5, 10.5.1, 10.5.2) they’ve got it right…maybe its been like this ever since the release of Leopard… But no matter what, we will fix this ourselves today 
Don’t worry if you never “fix” anything in your Mac before…its really simple…trust me…just follow the steps below and it will only take a few minutes!
Step 1: Open up System Preferences; click on Keyboard & Mouse, click on Keyboard Shortcuts; remove the tick in front of “Look up in Dictionary“, and then click on the “+” button at the bottom of the window:
Step 2: You should see a small drop down window that looks like this:
In the Menu Title section, type in “Look Up in Dictionary“. Do make sure that you get the case right, it has to be exactly the same as the one on the menu!
In the Keyboard Shortcut section, press a key combination that best suits you…I use Control + Command + A. If you can’t think of any or afraid to mess up others keyboard shortcuts, you can always use the default one (Control + Command + D). When are you ready, just press the Add button:
ONLY two steps…and you are done! If you’ve followed the steps correctly, your keyboard shortcut should appear immediately:
It should appear in your apps too:
It would be interesting to see how many builds does it take for Apple to fix this bug 
Awesome, this has been bugging me quite a bit. Thanks!
Thanks! It works now, though I learned about this shortcut in an Apple How-to Video that made it sound like you only needed to drag the cursor over a word and type command-control-D to get the dictionary, no selecting necessary, and if you just slide the cursor over another word the dictionary would change to that word. These functions don’t work, though I wish they did. Thanks again.
This is awesome. Finding this tiny error was almost impossible. You are a bond. I call this a Himalayan blunder..looks so tiny but a great mistake.
This is the first time I am ever posting a message on any site.
You made me to. I couldn’t resist but to appreciate your great help.
Thanks a ton.
Great tip! Maybe you can help me. My top keyboard shortcuts (volume up and down) stopped working when I reinstalled leopard.
How would you set them up in the shortcuts panel? I can’t find the option anywhere ?
Thanks!
Hi Chris, it would be great if you can send me an email so I can send you some instructions? Thanks!
p.s. my email address can be found in the “About Me” page at the top
thanks, i never noticed the capitalizing error, just wonder why it doesn’t work.
there’s another way to fix this, though: edit the file /System/Library/PreferencePanes/Keyboard.prefPane/Contents/Resources/English.lproj/DefaultConfigKeysTable.xml and change the “up” to “Up” there.
Hmm… I tried what you suggested and it works, but eventually
found documentation on the way to look up words without
even clicking on them, and that can be done using the
command-control D click that your instructions actually disable!
But command-control D didn’t work for me until I disabled,
as per your instructions, and then re-enabled it! Strange,
anyway both now work for me, thanks for point me the way
Thank you so much, small tip but very useful.
I think this is not a bug. If you use the menu item Look Up in Dictionary, the word appears in the dictionary application. If you use the stock shortcut, the word underneath the mouse pointer appears in a small box below the word.
Thanks for the tip. It was very helpful!