knock at (something)

knock at (something)

To strike something sharply and swiftly. Hush for a moment. I thought I heard someone knocking at the door. I was kept awake by the sound of tree branches knocking at the windows.
See also: knock

knock at something

to knock [on something] at a particular location. I could hear someone knocking at the door next to mine. Who is knocking at the door?
See also: knock