The Collaborative International Dictionary of English v.0.48:

Tackle \Tac"kle\ (?; sometimes improperly pronounced ?,
   especially by seamen), n. [OE. takel, akin to LG. & D. takel,
   Dan. takkel, Sw. tackel; perhaps akin to E. taw, v. t., or to
   take.]
   1. Apparatus for raising or lowering heavy weights,
      consisting of a rope and pulley blocks; sometimes, the
      rope and attachments, as distinct from the block, in which
      case the full appratus is referred to as a block and
      tackle.
      [1913 Webster]

   2. Any instruments of action; an apparatus by which an object
      is moved or operated; gear; as, fishing tackle, hunting
      tackle; formerly, specifically, weapons. "She to her
      tackle fell." --Hudibras.
      [1913 Webster]

   Note: In Chaucer, it denotes usually an arrow or arrows.
         [1913 Webster]

   3. (Naut.) The rigging and apparatus of a ship; also, any
      purchase where more than one block is used.
      [1913 Webster]

   Fall and tackle. See the Note under Pulley.

   Fishing tackle. See under Fishing, a.

   Ground tackle (Naut.), anchors, cables, etc.

   Gun tackle, the apparatus or appliances for hauling cannon
      in or out.

   Tackle fall, the rope, or rather the end of the rope, of a
      tackle, to which the power is applied.

   Tack tackle (Naut.), a small tackle to pull down the tacks
      of the principal sails.

   Tackle board, Tackle post (Ropemaking), a board, frame,
      or post, at the end of a ropewalk, for supporting the
      spindels, or whirls, for twisting the yarns.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

tackle \tac"kle\ n. (Football)
   1. An act of tackling[4]; as, brought down by a tackle by a
      lineman.
      [PJC]

   2. (Football) One of two linemen on a football team,
      occupying a position between the guard and an end; also,
      the position played by such a tackle.
      [PJC]

The Collaborative International Dictionary of English v.0.48:

Tackle \Tac"kle\, v. t. [imp. & p. p. Tackled; p. pr. & vb. n.
   Tackling.] [Cf. LG. takeln to equip. See Tackle, n.]
   1. To supply with tackle. --Beau. & Fl.
      [1913 Webster]

   2. To fasten or attach, as with a tackle; to harness; as, to
      tackle a horse into a coach or wagon. [Colloq.]
      [1913 Webster]

   3. To seize; to lay hold of; to grapple; as, a wrestler
      tackles his antagonist; a dog tackles the game.
      [1913 Webster]

            The greatest poetess of our day has wasted her time
            and strength in tackling windmills under conditions
            the most fitted to insure her defeat. --Dublin Univ.
                                                  Mag.
      [1913 Webster]

   4. (Football) To cause the ball carrier to fall to the
      ground, thus ending the forward motion of the ball and the
      play.
      [PJC]

   5. To begin to deal with; as, to tackle the problem.
      [PJC]

WordNet (r) 3.0 (2006):

tackle
    n 1: the person who plays that position on a football team; "the
         right tackle is a straight A student"
    2: gear consisting of ropes etc. supporting a ship's masts and
       sails [syn: rigging, tackle]
    3: gear used in fishing [syn: fishing gear, tackle, fishing
       tackle, fishing rig, rig]
    4: (American football) a position on the line of scrimmage; "it
       takes a big man to play tackle"
    5: (American football) grasping an opposing player with the
       intention of stopping by throwing to the ground
    v 1: accept as a challenge; "I'll tackle this difficult task"
         [syn: undertake, tackle, take on]
    2: put a harness; "harness the horse" [syn: harness, tackle]
       [ant: unharness]
    3: seize and throw down an opponent player, who usually carries
       the ball

Moby Thesaurus II by Grady Ward, 1.0:

258 Moby Thesaurus words for "tackle":
   accept, accouterments, amateur athlete, apparatus, appliances,
   appointments, approach, appurtenances, archer, armament, assume,
   athlete, attack, attempt, attend to, back band, backstrap,
   bag and baggage, baggage, ballplayer, baseballer, baseman, batter,
   battery, bearing rein, bellyband, bit, blinders, blinds, block,
   blocking back, bowman, breeching, bridle, buckle to, caparison,
   carry on, cat, catcher, cavesson, center, checkrein, cheekpiece,
   chinband, cinch, clobber, coach, collar, competitor, conduct,
   confront, consume, conveniences, cordage, cording, crab, crane,
   crank, crank in, cricketer, crownband, crupper, curb, deck tackle,
   defensive lineman, demolish, derrick, destroy, devour,
   differential tackle, dive into, do, draw in, draw taut, duffel,
   dunnage, embark in, embark upon, employ, end, endeavor, engage in,
   enter on, enter upon, equipage, equipment, erector, exercise, face,
   face up to, facilities, facility, fall, fall into, fall to,
   fall upon, fittings, fixtures, follow, footballer, forklift,
   furnishings, furniture, gag swivel, games-player, gamester,
   gantry crane, gear, get busy, get cracking, get going,
   get under way, get with it, girth, give a fling, give a go,
   give a try, give a whirl, go about, go at, go in for, go into,
   go to it, go upon, grapple with, guard, habiliments, hackamore,
   halter, hames, hametugs, harness, have at, headgear, headstall,
   hip straps, hoist, hop to it, hydraulic tailgate, impedimenta,
   infielder, installations, jack, jackscrew, jaquima, jerk line,
   jigger, jock, jump to it, jumper, kit, launch forth, launch into,
   lay about, lever, lift, lifter, light into, lineman, lines, luff,
   luggage, machinery, make a try, martingale, materiel, move into,
   munition, munitions, noseband, offensive lineman, outfield,
   outfielder, outfit, paraphernalia, pitch in, pitch into, plant,
   player, plumbing, plunge into, pole strap, poloist, practice,
   proceed to, professional athlete, prosecute, pugilist, pull in,
   pulley, purchase, pursue, quarterback, racer, reel, reel in, reins,
   ribbons, rig, rigging, ropework, roping, runner, running rigging,
   saddle, sail into, service, serving, set about, set at,
   set forward, set going, set to, set to work, shaft tug, sheave,
   side check, skater, snaffle, specialize in, sport, sportsman,
   stand up to, standing rigging, start in, stock-in-trade, surcingle,
   tack, tackling, tailback, take on, take to, take up, tauten,
   things, tighten, tools, toxophilite, trappings, traps, trim, tug,
   turn to, undertake, use, utensils, venture upon, wade into, wage,
   whipping, winch, wind in, windlass, wingback, winker braces,
   work at, wrestler, yoke