noun (n)

• a holder attached to the gunwale of a boat that holds the oar in place and acts as a fulcrum for rowing(noun.artifact)

  Synonym:
  oarlock, peg, pin, thole, tholepin
  

  source: wordnet30
• A contrivance or arrangement serving as a fulcrum for an oar in rowing. It consists sometimes of a notch in the gunwale of a boat, sometimes of a pair of pins between which the oar rests on the edge of the gunwale, sometimes of a single pin passing through the oar, or of a metal fork or stirrup pivoted in the gunwale and suporting the oar.(noun)

  source: webster1913