I recently updated my iPad Pro to iOS 9.3.3 and noticed that my dictionary always gives the message "No definition found".
This might have started earlier and I just didn't notice until now.
I tried selecting Manage from the bottom left of the empty dictionary message, however, I still get the same message and no dictionaries to add.
I already tried to restore my iPad with no success.
Now I updated it to 9.3.4 and the dictionary problem isn't fixed.
Best Answer
I had the same issue, to fix it go to this directory in your device: /var/MobileAsset/Assets.
There is a folder (com_apple_MobileAsset_DictionaryServices_dictionary2). Just replace the content of the folder from another apple device that has a working in-built dictionary. Make sure the other device has the same iOS version as your device. Of course, you need to jailbreak both devices in order to get root access to extract and replace the folder. That, or update to iOS 10 beta.
Hope that helps.