Dumb is the Old English word that means "mute, speechless," and itself came from an even older word dheubh meaning "confusion, stupefaction, dizziness." Today, dumb still means "unable to speak," but it doesn't have anything to do with intelligence. Its other meaning, however, does. More @Wikipedia
Hover over any link to get a description of the article. Please note that search keywords are sometimes hidden within the full article and don't appear in the description or title.