Oxford V1 API is deprecated.

[StewPoll]

So Oxford Dictionary API, that powers the !define plugin, released V2 of their API on 16th of April, and are shutting down their V1 API on June 30th.

They have a migration guide available here: https://developer.oxforddictionaries.com/version2

Looking at their response data, it looks like the only change needed is the new URL. to make the requests to, and to tell people that they need a different type of API Key. (As the Free API Key plan is no more, but Prototype should suit most people)