Creating an iOS Swift Application that gets synonyms and definitions for words entered by the user

Question

I am working on an iOS application using Swift that takes a word from a user and finds the synonyms for that word. It then offers to find the definitions for each of those synonyms.

I have done a lot of research but I have been having trouble finding any simple way to just access a thesaurus or dictionary using Swift and get synonyms or definitions. I am not interested in using the UIReferenceLibraryViewController since Apple is against much use of that and I hope to post my application on the App Store. I am aware that there are some dictionaries out there that are built using Objective-C, but I would be unsure of how to implement those in my (currently) Swift-only application.

I have found one API for Oxford dictionaries here that provides implementation for Swift, but there are a few hurdles (such as pricing and app keys that I don't have yet) that I am unsure about and am therefore curious if there are any other methods out there.

If anyone is aware of a simple way to access a thesaurus or dictionary through Swift to simply get a list of synonyms for a word or a definition of a word, I would greatly appreciate it. If there are no simple ways to do this but there are good instructions for a more complicated way to go about doing this, those would also be appreciated. Thanks!