A whip, first with three, then with six, and lastly with nine lashes, used for punishing offenders, and briefly called a cat. Lilburn was scourged, in 1637, with a whip having only three lashes, but there were twenty knots in each tail, and, as he received a lash every three paces between the Fleet and Old Palace Yard, Cook says that 60,000 stripes were inflicted. Titus Oates was scourged, in the reign of James II., with a cat having six lashes, and, between Newgate and Tyburn, received as many as 17,000 lashes. The cat-o'-nine-tails once used in the British army and navy is no longer employed there, but garotters and some other offenders are still scourged. Probably the punishment was first used on board ship, where ropes would be handy, and several ropes are called cats, as “cat-harpings,” for bracing the shrouds, “cat-falls,” which pass over the cat-head and communicate with the cat-block. etc. The French martinet (q.v.) had twelve leather thongs.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894