How to prevent Nightbot from using Blacklisted Words

Hiya, what do you mean? You control what Nightbot says in your commands.

I have commands that pull from external API's including urbandictionary, and it would be great if I could filter / prevent it from bringing back certain words.

I see, nightbot is not checking it's own output for blacklisted words. What you can do is build a layer between nightbot and your data source and filter the results you want, or swap to a different source for your data.