Any coarse woollen or hempen yarn. It is used for mops, &c., in the cabins; also for mats, which are worked on canvas with a large bolt-rope needle.
♦ To thrum. A vessel, when leaky, is thrummed by working some heavy spare sail, as the sprit-sail, into a thrummed mat, greasing and tarring it well, passing it under the bottom, and heaving all parts tight. The pressure forces the tarred oakum into the openings, and thus, in part, arrests the ingress of water.