When we look up the meaning of any word through Spotlight:
There is no 'source' information.
Even the Dictionary.app, which Spotlight uses, does not show the source.
The best I can find so far is to disable / enable different Dictionaries in Dictionary.app's Preferences, until the definition disappears / changes, to figure out from what dictionary the meaning is from.
How can I see where the definition comes from without this pain?