#1 dumb s. [dense, dim, dull, obtuse, slow] slow to learn or understand; lacking intellectual acuity; "so dense he never understands anything I say to him"; "never met anyone quite so dim"; "although dull at classical learning, at mathematics he was uncommonly quick"- Thackeray; "dumb officials mak. wn
#2 dumb s. [speechless] temporarily incapable of speaking; "struck dumb"; "speechless with shock". wn
#3 dumb s. lacking the power of human speech; "dumb animals". wn
#4 dumb s. [mute, silent] unable to speak because of hereditary deafness. wn
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