"iron hook for fastening one thing to another," late 13c., from Old French grapil "hook" (see grapnel).
1520s, "seize and hold fast," originally in reference to a ship, by means of a grapple, from grapple (n.). Extended sense of "battle, struggle in close contact" (usually with with) is from 1580s of persons, 1630s of immaterial things. Related: Grappled; grappling. Grappling hook is from 1620s.