rap someone's knuckles

English

rap someone's knuckles (third-person singular simple present raps someone's knuckles, present participle rapping someone's knuckles, simple past and past participle rapped someone's knuckles)

(literally) to tap one's knuckles on an object such as a desk or wall to attract attention or as a signal of commmunication.
Just rap your knuckles on the wall when you're ready to go.
- 2012, Michael Kardos, The Three-Day Affair: A Novel‎^[1], →ISBN, page PT65:
  The professor let this go for a moment, then began to rap his knuckles on the podium until the room quieted again.
(somewhat dated, idiomatic) to give someone a punishment.
If the sales department doesn't get organized soon, the CEO is going to rap their knuckles.
- 2015, James G. Greenlee, “Crazy Quilt”, in McMaster University, Volume 3: 1957-1987: A Chance for Greatness‎^[2], →ISBN, page 308:
  ... while political science at Western had received a sharp rap across its knuckles.
(archaic, literally) to strike someone on the back of the hand usually as a method of punishment.
In the old days the teacher would rap someone's knuckles with a ruler if they misbehaved in class.
- 2011, Lisa Plumley, chapter 7, in Outlaw‎^[3], →ISBN, page PT45:
  ...she commanded, sounding for all the world like a mean old schoolmarm about to rap his knuckles with her ruler.