[1] : 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'eon, 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.
      1913 webster

   2. to pull; to pluck. obs.
      1913 webster

            to ease the pain,
            his tugged cars suffered with a strain. --hudibras.
      1913 webster
see also:
tugged tugging duke team tie touch 
tow tuck toy 

[2] : WordNet (r) 2.0

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
     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
see also:
jerk tugboat towboat tower labor labour 
push drive lug tote tugging 
tugged 

[3] : WordNet (r) 2.0

tugging
     see tug
see also:
tug 

Tugging >> T Words
Tugging, definition of term: Tugging
tugging_pag1.html