(nautical) A scourge (multi-tail whip) having nine, often knotted, whipcords, formerly used for flogging as naval punishment.

(mathematics, computing theory) A particular notation which describes the limiting behavior of a function when the argument tends towards a particular value or infinity, usually in terms of simpler functions. Useful in the analysis of algorithms.

plural of cat-o'-nine-tails

(rare) Short for cat-o'-nine-tails.

Alternative spelling of cat-o'-nine, which is short for cat-o'-nine-tails.