Source : Webster's Revised Unabridged Dictionary (1913)

Oarlock \Oar"lock`\ ([=o]r"l[o^]k`), n. (Naut.),
   The notch, fork, or other device on the gunwale of a boat, in
   which the oar rests in rowing. See {Rowlock}.

Source : WordNet®

oarlock
     n : a holder attached to the gunwale of a boat that holds the
         oar in place and acts as a fulcrum for rowing [syn: {peg},
          {pin}, {thole}, {tholepin}, {rowlock}]