Then infogeeks2 solution may solve the issue for you like it did for others. ”I had the same problem. I deleted the files:
com.apple.Dictionary.plist
com.apple.DictionaryServices.plist
from the Users/…/Library/Preferences folder.
After that, Dictionary.app took a long time to launch the first time but launched instantly after that until I changed the Dictionary.app preferences.
The Dictionary Preferences pane took a long time to open or would hang. Dictionary.app opened instantly if I did not change any preferences. If I changed the preferences, Dictionary.app would again be slow to startup, even after restarting Dictionary.app repeatedly. Deleting the .plist files seems to fix the problem but I can’t change Dictionary preferences without the problem re-occuring.”