The Collaborative International Dictionary of English v.0.48:

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.
      [1913 Webster]

            He tugged, he shook, till down they came. --Milton.
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   2. To labor; to strive; to struggle.
      [1913 Webster]

            England now is left
            To tug and scamble and to part by the teeth
            The unowed interest of proud-swelling state. --Shak.
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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.
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   2. A sort of vehicle, used for conveying timber and heavy
      articles. [Prov. Eng.] --Halliwell.
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   3. (Naut.) A small, powerful steamboat used to tow vessels;
      -- called also steam tug, tugboat, and towboat.
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   4. A trace, or drawing strap, of a harness.
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   5. (Mining.) An iron hook of a hoisting tub, to which a
      tackle is affixed.
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   Tug iron, an iron hook or button to which a tug or trace
      may be attached, as on the shaft of a wagon.
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The Collaborative International Dictionary of English v.0.48:

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.
      [1913 Webster]

            There sweat, there strain, tug the laborious oar.
                                                  --Roscommon.
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   2. To pull; to pluck. [Obs.]
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            To ease the pain,
            His tugged cars suffered with a strain. --Hudibras.
      [1913 Webster]

WordNet (r) 3.0 (2006):

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

Moby Thesaurus II by Grady Ward, 1.0:

121 Moby Thesaurus words for "tug":
   adduct, adduction, affinity, allurement, attract, attractance,
   attraction, attractiveness, attractivity, back band, backstrap,
   battle, be magnetic, bearing rein, bellyband, bit, blinders,
   blinds, breeching, bridle, caparison, capillarity,
   capillary attraction, cavesson, centripetal force, checkrein,
   cheekpiece, chinband, cinch, collar, crownband, crupper, curb,
   draft, drag, draggle, draw, draw towards, drive, fight, gag swivel,
   girth, gravitation, gravity, hackamore, hale, halter, hames,
   hametugs, harness, haul, have an attraction, headgear, headstall,
   heave, hip straps, jaquima, jerk line, lines, lug, lure, magnet,
   magnetism, magnetize, martingale, moil, mutual attraction,
   noseband, oppugn, overexert, overexertion, overextend,
   overextension, overstrain, overstress, overtax, overtaxing,
   pole strap, press, pull, pull towards, pulling power, rack, reins,
   ribbons, saddle, shaft tug, side check, snaffle, snake, strain,
   strain every nerve, straining, stress, stress and strain,
   stressfulness, stretch, strive, surcingle, sweat blood, sympathy,
   tack, tackle, take in tow, tax, taxing, tense, tension, toil, tow,
   traction, trail, train, trappings, trawl, troll, war, warfare,
   winker braces, work, yoke



V.E.R.A. -- Virtual Entity of Relevant Acronyms (February 2016):

TUG
       TeX User's Group (org., user group, TeX)