Oakum \Oak"um\, n. [AS. [=a]cumba; pref. ? (cf.G. er-, Goth. us-, orig. meaning, out) + cemban to comb, camb comb. See {Comb}.] 1. The material obtained by untwisting and picking into loose fiber old hemp ropes; -- used for calking the seams of ships, stopping leaks, etc. 2. The coarse portion separated from flax or hemp in nackling. --Knight. {White oakum}, that made from untarred rope.