- (old, no longer used) Not able to speak. If someone is dumb they can not say anything.
- They went to a school for the deaf and dumb.
- Dogs are just dumb animals.
- (informal) Another word for stupid. If you are dumb you are not intelligent.
- That is a really dumb idea.
- How could I be so dumb? I know better than that!
- I'm not dumb enough to believe that.
- It is not nice to call someone dumb.
Using dumb for someone who cannot speak is not polite. It is seen as an insult to people who cannot speak. That was the first meaning, but now dumb usually means stupid. "Deaf and dumb" is also not polite, and it upsets people who are deaf.