Word Study
cat o' nine tails
CIDE DICTIONARY
cat o' nine tails, n.
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. [WordNet 1.5]
For further exploring for "cat o' nine tails" in Webster Dictionary Online