towboat \tow"boat`\, n.
   1. a vessel constructed for being towed, as a canal boat.
      1913 webster

   2. a steamer used for towing other vessels; a tug.
      1913 webster

tug \tug\, n.
   1. a pull with the utmost effort, as in the athletic contest
      called tug of war; a supreme effort.
      1913 webster

            at the tug he falls,
            vast ruins come along, rent from the smoking walls.
                                                  --dryden.
      1913 webster

   2. a sort of vehicle, used for conveying timber and heavy
      articles. prov. eng. --halliwell.
      1913 webster

   3. naut. a small, powerful steamboat used to tow vessels;
      -- called also steam tug, tugboat, and towboat.
      1913 webster

   4. a trace, or drawing strap, of a harness.
      1913 webster

   5. mining. an iron hook of a hoisting tub, to which a
      tackle is affixed.
      1913 webster

   tug iron, an iron hook or button to which a tug or trace
      may be attached, as on the shaft of a wagon.
      1913 webster
see also:
steam tug tugboat towboat tug iron 

towboat
     n : a powerful small boat designed to pull or push larger ships
         syn: tugboat, tug, tower
see also:
tugboat tug tower