backward, birdbrained, defective, dim, dim-witted, dopey, dull, dumbbell, dumbo, dumdum, dummy, exceptional, feeble-minded,
gorked, half-witted, held back, imbecile, lamebrained, mentally defective, moronic, numbskull, opaque, pinhead, retardo, sappy, simple, simple-minded, slow, slow-witted, stupid, subnormal, touched, underachieving, weak, yo-yo, impaired, inarticulate, incoherent, mousy, mum, mute, quiet, silent, soundless, speechless,
tongue-tied,
uncommunicative, wordless.
