old-fashioned To remain vigilant or carefully watchful (for something or someone); to act as a guard or watch. The gang employed youths from the area to keep nit during a drug deal and give a signal if any police officers arrived. I offered to keep nit at the door, as I had no intention of risking my life in that creepy old house.
keep nitkeep watch or act as a guard. Australian
Nit here is possibly an alteration of nix , a warning signal by schoolchildren that a teacher is approaching.