dumb
     adj 1: 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 make some really
            dumb decisions"; "he was either normally stupid or
            being deliberately obtuse"; "worked with the slow
            students" [syn: {dense}, {dim}, {dull}, {obtuse}, {slow}]
     2: unable to speak temporarily; "struck dumb"; "speechless with
        shock" [syn: {speechless}]
     3: lacking the power of human speech; "dumb animals"
     4: unable to speak because of hereditary deafness [syn: {mute},
         {silent}]
Source: WordNet® 2.0