The Collaborative International Dictionary of English v.0.48:

Grapnel \Grap"nel\, n. [OE. grapenel, dim. fr. F. grappin the
   grapple of a ship; of German origin. See Grape.] (Naut.)
   A small anchor, with four or five flukes or claws, used to
   hold boats or small vessels; hence, any instrument designed
   to grapple or hold; a grappling iron; a grab; -- written also
   grapline, and crapnel.
   [1913 Webster]

WordNet (r) 3.0 (2006):

grapnel
    n 1: a tool consisting of several hooks for grasping and
         holding; often thrown with a rope [syn: grapnel,
         grapple, grappler, grappling hook, grappling iron]
    2: a light anchor for small boats [syn: grapnel, grapnel
       anchor]