knocker
nounUK /ˈnɒk.ər/
US /ˈnɑː.kɚ/
A knocker is a metal ring or handle on a door that you use to knock.
She lifted the brass knocker and tapped it twice.
OTHER MEANINGS
2. A person who knocks on a door.
The knocker at the gate asked to see the manager.
3. A person who criticizes something constantly.
He is a constant knocker of the new rules.
4. In British English, a rude slang word for a woman's breasts.
The comedian made a joke using the word knocker.