[1] : The Collaborative International Dictionary of English v.0.48

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 

[2] : The Collaborative International Dictionary of English v.0.48

tugboat \tug"boat`\, n.
   see tug, n., 3.
   1913 webster
see also:
tug 

[3] : WordNet (r) 2.0

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

Tugboat >> T Words
Tugboat, definition of term: Tugboat
tugboat_pag1.html