tree·nail /ˈtrʌnḷ/
  木栓
  Tree·nail n.  Shipbuilding A long wooden pin used in fastening the planks of a vessel to the timbers or to each other. [Written also trenail, and trunnel.]
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  treenail
       n : a wooden peg that is used to fasten timbers in shipbuilding;
           water causes the peg to swell and hold the timbers fast
           [syn: trenail, trunnel]