dumb

aphonic banal blockheaded brainless dense denser dim dim-witted dimmer dimwitted dizzy doltish dopey dull duller dumbfounded empty feeble-minded half-baked hushed idiotic inarticulate incommunicable incommunicative incoherent inobtrusive insensate moronic most vacuous oafish obtuse quietest quieten quiet quieter quietened reeling retarded shush silent silence simpler simpleminded simple slow slower slowest speechless stolid stupid taciturn thick thickheaded thick-witted tight-lipped tightlipped uncommunicable unintelligent vacuous voiceless voiceless witless zany