1. obsolete slang A police officer or detective. (i.e., someone who "nails" criminals.) A couple of nailers came snooping around the offices the other day, but I had hidden anything incriminating well before they arrived. The boss lost a bit of trust in me ever since my younger brother became a nailer.

2. dated slang Someone who excels at some activity or task. Suzy has always been a nailer when it comes to her schoolwork—I don't think there's ever been a year that she wasn't top of her class. The young draft pick from Wisconsin has been an absolute nailer as the Vikings' new kicker.