A long pole with a large, sharp barb on the end, which is tied to a long length of rope. Once harpoons were used by sailors to attack whales, which pulled all the rope out of the longboat and then dragged the boat behind them until they got shagged out. Sometimes they rocked the boat and sailors drowned. Later harpoons were fired from cannons aboard the sailing ship, a technological development welcomed by the sailor's union. See Moby Dick; poon.