Today, most of the time someone or something is described as dumb when it shows a lack of thought, like your dumb idea of wearing flip-flops in a snowstorm. 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.