rap someone's knuckles

Definitions

1. to tap one's knuckles on an object such as a desk or wall to attract attention or as a signal of commmunication.
   literally
2. to give someone a punishment.
   dated, idiomatic
3. to strike someone on the back of the hand usually as a method of punishment.
   archaic, literally

Examples

“Just rap your knuckles on the wall when you're ready to go.”

“The professor let⟳ this go for a moment, then began to rap his knuckles on the podium until the room quieted again.”

“If the sales department doesn't get⟳ organized soon, the CEO is going to rap their knuckles.”

“... while political science at Western had received a sharp rap across its knuckles.”

“In the old days the teacher would rap someone's knuckles with a ruler if they misbehaved in class.”

“...she commanded, sounding for all the world like⟳ a mean⟳ old schoolmarm about to rap his knuckles with her ruler.”

CEFR level