Source : Webster's Revised Unabridged Dictionary (1913)

Tug \Tug\, v. t. [imp. & p. p. {Tugged}; p. pr. & vb. n.
   {Tugging}.] [OE. toggen; akin to OD. tocken to entice, G.
   zucken to jerk, draw, Icel. toga to draw, AS. t['e]on, p. p.
   togen, to draw, G. ziehen, OHG. ziohan, Goth. tiuhan, L.
   ducere to lead, draw. Cf. {Duke}, {Team}, {Tie}, v. t.,
   {Touch}, {Tow}, v. t., {Tuck} to press in, {Toy} a
   plaything.]
   1. To pull or draw with great effort; to draw along with
      continued exertion; to haul along; to tow; as, to tug a
      loaded cart; to tug a ship into port.

            There sweat, there strain, tug the laborious oar.
                                                  --Roscommon.

   2. To pull; to pluck. [Obs.]

            To ease the pain, His tugged cars suffered with a
            strain.                               --Hudibras.

Tug \Tug\, v. i.
   1. To pull with great effort; to strain in labor; as, to tug
      at the oar; to tug against the stream.

            He tugged, he shook, till down they came. --Milton.

   2. To labor; to strive; to struggle.

            England now is left To tug and scamble and to part
            by the teeth The unowed interest of proud-swelling
            state.                                --Shak.

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

            At the tug he falls, Vast ruins come along, rent
            from the smoking walls.               --Dryden.

   2. A sort of vehicle, used for conveying timber and heavy
      articles. [Prov. Eng.] --Halliwell.

   3. (Naut.) A small, powerful steamboat used to tow vessels;
      -- called also {steam tug}, {tugboat}, and {towboat}.

   4. A trace, or drawing strap, of a harness.

   5. (Mining.) An iron hook of a hoisting tub, to which a
      tackle is affixed.

   {Tug iron}, an iron hook or button to which a tug or trace
      may be attached, as on the shaft of a wagon.

Source : WordNet®

tug
     n 1: a sudden abrupt pull [syn: {jerk}]
     2: a powerful small boat designed to pull or push larger ships
        [syn: {tugboat}, {towboat}, {tower}]
     [also: {tugging}, {tugged}]

tug
     v 1: pull hard; "The prisoner tugged at the chains"; "This movie
          tugs at the heart strings"
     2: strive and make an effort to reach a goal; "She tugged for
        years to make a decent living"; "We have to push a little
        to make the deadline!"; "She is driving away at her
        doctoral thesis" [syn: {labor}, {labour}, {push}, {drive}]
     3: tow (a vessel) with a tug; "The tugboat tugged the freighter
        into the harbor"
     4: carry with difficulty; "You'll have to lug this suitcase"
        [syn: {lug}, {tote}]
     5: move by pulling hard; "The horse finally tugged the cart out
        of the mud"
     6: pull or strain hard at; "Each oar was tugged by several men"
     7: struggle in opposition; "She tugged and wrestled with her
        conflicts"
     [also: {tugging}, {tugged}]