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.

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}]

tugging
     See {tug}