Dumb

adjective

1. Unable to speak; lacking power of speech (kept in "deaf, dumb, and blind").

   "His younger brother was born dumb, and communicated with sign language."

2. Silent; unaccompanied by words.

   "dumb show"

3. (especially of a person) Extremely stupid.

   "You are so dumb! You don't even know how to make toast!"

4. Pointless, foolish, lacking intellectual content or value.

   "Brendan had the dumb job of moving boxes from one conveyor belt to another."

5. Lacking brightness or clearness, as a colour.