If you have ever mistakenly added a word to the Brave browser dictionary,
you need to manually edit the Custom Dictionary.txt
file.
As of March 2020, the Brave UI lacks a feature to do this.
This will depend on your OS. Google for where this is on your OS.
The file on macOS is at: ~/Library/Application\ Support/BraveSoftware/Brave-Browser/Default/Custom\ Dictionary.txt
.
Use your favorite text editor to edit and save the file.
I tried totally deleting the file and my previously saved dictionary (including the word I want to remove) still appear to now squiggle in Brave.
It also adds it here, and I have removed it from the list, but it still is stuck and won't re-squiggle :)