SharePoint 2010 Publishing Sites have a cool spell check feature for page content but it is not at all obvious how to add words your own words to the dictionary. Unlike most modern word processors there is no “Add to Dictionary” button on the GUI.

Instead you need to:

1. Create a text file called “Custom Dictionary.txt” with your list of words to add to the Spell Checker, one per line.
2. Add a new document library to root of the site collection called “Spelling”.
3. Upload your called “Custom Dictionary.txt” to the “Spelling” library.

What could be more intuitive eh?