What does "harpoon" mean?

Harpoon: A spear or javelin used to strike and kill large fish, as whales; a harping iron. It consists of a long shank, with a broad, fiat, triangular head, sharpened at both edges, and is thrown by hand, or discharged from a gun. Harpoon fork, a kind of hayfork, consisting of bar with hinged barbs at one end a loop for a rope at the other end, used for lifting hay from the load by horse power. -- Harpoon gun, a gun used in the whale fishery for shooting the harpoon into a whale.