Excalibur flags any word that is not in an active dictionary. To add the flagged word to an active dictionary, hit the Add... button. You can add the word to any active dictionary that is modifiable. The Standard Dictionary is read only.
Use the checkbox to always select the same dictionary for the word you are spell checking. When you do this, Excalibur will stop presenting the Add dialog every time you add a word. If you have checked this box, you can force Excalibur to bring up the dialog by holding the shift key down while you click on Add. This allows you to deselect the checkbox or select a new set of dictionaries to automatically select from then on.
After adding a word to a dictionary, you will still have to take an action on the current word. It will often be the case that you would like to simply ignore the word now that you have entered it into a dictionary. You can use the Options menu to make this the default action.
Note: In order for the Add... button to be operational, you must have at least one modifiable dictionary that is active. A dictionary is not modifiable if its name appears in italics in the Dictionary menu. A dictionary is active if it is checked.