verb / noun
knock
NAHK/nɑːk/
A sharp blow or the sound it produces.
She knocks on the wooden door to get someone's attention.

Etymology
Cnocian already included knocking on a door, so the attention-getting action continues an old meaning. The word is likely imitative, echoing the sound of a blow.
In context
I'll hold on to my isolator. Give it a couple thumps. And just knock all that rust off of there.
More examples
- Three sharp knocks at the door wake me.
- Her only knock on the apartment is its tiny kitchen.
- His confidence takes a knock after the rejection.
- The engine knocks whenever I accelerate.
Forms
knock · knocks · knocked · knocking
knocker noun — A door fixture struck to announce visitors.