Source : Webster's Revised Unabridged Dictionary (1913)

Underrun \Un`der*run"\, v. t.
   To run or pass under; especially (Naut.), to pass along and
   under, as a cable, for the purpose of taking it in, or of
   examining it.

   Note: The cable passes over the bows and stern of the boat
         used, while the men haul the boat along by pulling upon
         the cable. --Totten.

   {To underrun a tackle} (Naut.), to separate its parts and put
      them in order.