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," possibly of Germanic origin, or from Latin harpa- "hook" (cf. harpagonem "grappling hook," from Greek *harpagon, related to harpe "sickle"). Earlier harping-iron (mid-15c.). Sense and spelling perhaps influenced by Dutch (cf. Middle Dutch harpoen) or Basque, the language of the first whaling peoples, who often accompanied English sailors on their early expeditions. Also see -oon.
1774, from harpoon (n.). Related: Harpooned; harpooning. For agent-noun forms, harpooner is from 1726; harpooneer from 1610s.