rap someone's knuckles

Verb

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)

1. (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.
   • The professor let this go for a moment, then began to rap his knuckles on the podium until the room quieted again.2012, Michael Kardos, The Three-Day Affair: A Novel, →ISBN, page PT65
2. (dated, idiomatic) to give someone a punishment.
   • 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.2015, James G. Greenlee, “Crazy Quilt”, in McMaster University, Volume 3: 1957-1987: A Chance for Greatness, →ISBN, page 308
3. (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.
   • ...she commanded, sounding for all the world like a mean old schoolmarm about to rap his knuckles with her ruler.2011, Lisa Plumley, chapter 7, in Outlaw, →ISBN, page PT45