Although Office has its own dictionary, it probably does not contain all the words and jargon that you use. If this is the case, you can add your own frequently used terms, and names to the dictionary.
From the Tools menu, click Options (See link below for 2007)
Select the Spelling and Grammar tab
Click the Custom Dictionaries button
Place a check beside the dictionary you want to modify
Click the Modify button
In the Word field, type in the word you want to add to the dictionary and click the Add button Click OK
Click OK to close the Custom Dictionaries dialog box
Click OK to close the Options dialog box
If you want to remove a word from the dictionary, complete steps 1 through 7. Select the word you want to remove and click the Delete button.
The Custom.dic file is a text file. You can create it or edit it using notepad.
Multiple dictionaries can be created for special purposes, like a list of employee names.
The Custom.dic file is used by all of the Office applications that do Spell checking.