This is now available on Google Docs
I added a word to my custom dictionary whilst using Google Docs accidentally. Guess what? From what I can tell, you can not edit the custom dictionary to remove words that you have added by accident.
This is a really big problem when Google Docs is being used for academic work (such as when I use it for my Open University TMAs).
Imagine running a spell check and it coming up without errors, but you have previously added an incorrect word to the dictionary - it is likely that you would type this word incorrectly again too.
Google, please get your act together and sort out a way of doing this. I may have to move back to Libre Office on my Ubuntu machine until this is sorted out - although I would rather use my Chromebook!