Cat o' nine tails, cat-o'-nine-tails n. 1. a whip used as an instrument of punishment consisting of nine pieces of knotted line or cord fastened to a handle; -- formerly used to flog offenders on the bare back; -- called also the cat. It was used in the British Navy to maintain discipline on board sailing ships.
Syn. -- cat.
[WordNet 1.5 +PJC]