The addition of -ity to an adjective results in a shift of stress to the antepenultimate syllable; that is, words in -ity are stressed on the last syllable before the -ity, even in cases where this syllable is part of another suffix (as in words in -ability and -icity).
adjective, dumber, dumbest. 1. lacking intelligence or good judgment; stupid; dull-witted. 2. lacking the power of speech (offensive when applied to humans): a dumb animal.
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.