In the Check Spelling dialog box, click Dictionaries.
In the Dictionaries dialog box, in the Current Custom dictionary list, select Manage Custom Dictionaries.
In the Custom Dictionaries list, click Add and browse to the dictionary’s location. To create a new custom dictionary, click New and enter the dictionary’s name. The name must contain the .cus extension.
Click OK. The newly selected dictionary is highlighted as the current custom dictionary.
If you would like to import a word list into your custom dictionary, click Import.