YOU SHOULD NOT DO THIS but you know that little dictionary word lookup feature in iOS? It’s called UIReferenceLibraryViewController, you can use it and its public, but you can also strip mine it for the dictionary definitions.

Don't do it though since:
- You don’t have the rights to use the Oxford dictionary
- This is super undocumented and will probably get you rejected from App Review
- This could break at any time if they decide to lock this down

...but it is technically possible. Don’t.