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.
dumb. adj. 1. (Pathology) lacking the power to speak, either because of defects in the vocal organs or because of hereditary deafness. 2. lacking the power of human speech: dumb animals. 3. temporarily lacking or bereft of the power to speak: struck dumb.