By default, Word automatically checks spelling and grammar as you write your document. It displays any errors it finds as wavy and green red underlines. While they have their value, these can adversely affect your computer’s performance as they continually demand memory.
To turn off automatic spelling and grammar checking:
On the Tools menu, click Options, and then click the Spelling & Grammar tab.
Clear the Check spelling as you type checkbox.
Clear the Check grammar as you type checkbox.