dumb

adjective

1. 1

   unable to speak because of hereditary deafness

2. 2

   lacking the power of human speech

   dumb animals

3. 3

   temporarily incapable of speaking

   struck dumb

   speechless with shock

4. 4

   slow to learn or understand; lacking intellectual acuity

   so dense he never understands anything I say to him

   never met anyone quite so dim