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.
Word Origin & History. dumb O.E. dumb silent, unable to speak, from PIE *dheubh- confusion, stupefaction, dizziness.. O.E., Goth. (thumb) and O.N. (dumbr) forms meant only mute, speechless; in O.H.G. (thumb) it meant both this and stupid, and in Mod.Ger. this latter became the only sense. Meaning foolish, ignorant was occasionally in English from early 14c., but modern use (1823) comes from influence of Ger.