1610s, from French harpon, from Old French harpon "cramp iron, clamp, clasp" (described as a mason's tool for fastening stones together), from harper "to grapple, grasp," which is of uncertain origin. It is possibly of Germanic origin; or the French word might be from Latin harpa "hook" (related to harpagonem "grappling hook"), from Greek harpe "sickle," from PIE root *serp- (1) "sickle, hook." Earlier word for it was harping-iron (mid-15c.). Sense and spelling perhaps influenced by Dutch (compare Middle Dutch harpoen) or Basque, the language of the first European whaling peoples, who often accompanied English sailors on their early expeditions. Also see -oon.
1747, from harpoon (n.). Related: Harpooned; harpooning. Agent-noun form harpooner is from 1726; harpooneer from 1610s.