Add or edit words in a spell check dictionary - Office Support

 support.office.com/en-us/arti…

In Office, you can add words, such as proper names or technical terms, to custom dictionaries so that they aren't marked as misspelled.Learn how to find the Custom Dictionaries dialog box, where you can add words, add or create new custom dictionaries, change the default dictionary, and edit word lists in custom dictionaries.

Open link