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 (comparative dumber, superlative dumbest) ( 1 dated) Unable to speak; lacking power of speech (kept in deaf, dumb, and blind). ( 2 dated) Silent; unaccompanied by words. ( 3 informal, pejorative, especially of a person) extremely stupid. ( figuratively) Pointless, foolish, lacking intellectual content or value.