rap someone's knuckles

present singular third person raps someone's knuckles · participle present rapping someone's knuckles · participle past rapped someone's knuckles · past rapped someone's knuckles

1. literallyto 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.

   1 more example

   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. datedidiomaticto give someone a punishment.

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

   1 more example

   ... 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. archaicliterallyto 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.

   1 more example

   ...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