Word displays the Custom Dictionaries dialog box. In Word 2010 display the File tab of the ribbon and then click Options.) (In Word 2007 click the Office button and then click Word Options. You can check the language of your dictionary in this manner: Word keeps track of the language of both your text and allows you to specify with what language a dictionary should be associated. The most likely cause for this situation is that the language of the word you are trying to add doesn't match the language of the dictionary. However, when he right-clicks on the word in order to add it to the dictionary, he finds the 'add to dictionary' option grayed out, so that he cannot add it.
Richard notes that when doing a spelling check in the background, Word dutifully underlines words it thinks are spelled incorrectly.
