Unable to speak; lacking power of speech (kept in "deaf, dumb, and blind").
Example: "His younger brother was born dumb, and communicated with sign language."
Silent; unaccompanied by words.
Example: "Dumb show"
(especially of a person) extremely stupid.
Example: "You are so dumb! you don't even know how to make toast!"
Pointless, foolish, lacking intellectual content or value.
Example: "Brendan had the dumb job of moving boxes from one conveyor belt to another."
Lacking brightness or clearness, as a colour.