If you are referring to the AutoComplete suggestion (which only works for
dates in Word), you can turn it off by running a little macro. Press Alt+F11
to display the Visual Basic Editor. Press Ctrl+G to activate the Immediate
window. Type
Application.DisplayAutoCompleteTips = False
and press Enter.
If you are referring to the text which appears when you rest the mouse
pointer on a button on a ribbon tab, choose the "Don't show ScreenTips"
option in the "ScreenTip style" box (Office button | Word Options, Popular
category).