10.6: Force Dictionary to show definitions in one window 
Wed, Sep 30 2009 at 7:30AM PDT • Contributed by: robg

Wed, Sep 30 2009 at 7:30AM PDT • Contributed by: robg

The new feature, if you haven't noticed, is that Dictionary will open a new window each time you use the Open in Dictionary service (in the Services menu, or by Control-clicking on a word in a Services-aware application). If you look up a lot of words, this gets old really fast. Based on seeing my name in the Tweet, I took the bait, and went looking for an answer. For the first time in Snow Leopard, that means I used the hard method of finding hidden preferences. It wasn't actually all that hard, and I managed to find the fix in only a couple of minutes (thanks, arcticmac, for that well-written how-to!).
If you'd prefer Dictionary not open a new window every time you look up a word using Services, quit Dictionary if it's running, open Terminal, and enter this command:
defaults write com.apple.Dictionary ProhibitNewWindowForRequest -bool TRUE
From now on, words looked up via Services will open in the same Dictionary window. Reverse this behavior by changing TRUE to FALSE in the above, or if you're a purist, with defaults delete com.apple.Dictionary ProhibitNewWindowForRequest. This works perfectly for me, and I'll be expecting that new Ferrari in the driveway by Friday, @luomat!