The Collaborative International Dictionary of English v.0.48:

Rub \Rub\, v. t. [imp. & p. p. Rubbed; p. pr. & vb. n.
   Rubbing.] [Probably of Celtic origin; cf. W. rhwbiaw, gael.
   rub.]
   1. To subject (a body) to the action of something moving over
      its surface with pressure and friction, especially to the
      action of something moving back and forth; as, to rub the
      flesh with the hand; to rub wood with sandpaper.
      [1913 Webster]

            It shall be expedient, after that body is cleaned,
            to rub the body with a coarse linen cloth. --Sir T.
                                                  Elyot.
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   2. To move over the surface of (a body) with pressure and
      friction; to graze; to chafe; as, the boat rubs the
      ground.
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   3. To cause (a body) to move with pressure and friction along
      a surface; as, to rub the hand over the body.
      [1913 Webster]

            Two bones rubbed hard against one another.
                                                  --Arbuthnot.
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   4. To spread a substance thinly over; to smear.
      [1913 Webster]

            The smoothed plank, . . .
            New rubbed with balm.                 --Milton.
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   5. To scour; to burnish; to polish; to brighten; to cleanse;
      -- often with up or over; as, to rub up silver.
      [1913 Webster]

            The whole business of our redemption is to rub over
            the defaced copy of the creation.     --South.
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   6. To hinder; to cross; to thwart. [R.]
      [1913 Webster]

            'T is the duke's pleasure,
            Whose disposition, all the world well knows,
            Will not be rubbed nor stopped.       --Shak.
      [1913 Webster]

   To rub down.
      (a) To clean by rubbing; to comb or curry; as, to down a
          horse.
      (b) To reduce or remove by rubbing; as, to rub down the
          rough points.

   To rub off, to clean anything by rubbing; to separate by
      friction; as, to rub off rust.

   To rub out, to remove or separate by friction; to erase; to
      obliterate; as, to rub out a mark or letter; to rub out a
      stain.

   To rub up.
      (a) To burnish; to polish; to clean.
      (b) To excite; to awaken; to rouse to action; as, to rub
          up the memory.
          [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Rub \Rub\, n. [Cf. W. rhwb. See Rub, v,t,]
   1. The act of rubbing; friction.
      [1913 Webster]

   2. That which rubs; that which tends to hinder or obstruct
      motion or progress; hindrance; obstruction, an impediment;
      especially, a difficulty or obstruction hard to overcome;
      a pinch.
      [1913 Webster]

            Every rub is smoothed on our way.     --Shak.
      [1913 Webster]

            To sleep, perchance to dream; ay, there's the rub.
                                                  --Shak.
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            Upon this rub, the English ambassadors thought fit
            to demur.                             --Hayward.
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            One knows not, certainly, what other rubs might have
            been ordained for us by a wise Providence. --W.
                                                  Besant.
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   3. Inequality of surface, as of the ground in the game of
      bowls; unevenness. --Shak.
      [1913 Webster]

   4. Something grating to the feelings; sarcasm; joke; as, a
      hard rub.
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   5. Imperfection; failing; fault. [Obs.] --Beau. & Fl.
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   6. A chance. [Obs.]
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            Flight shall leave no Greek a rub.    --Chapman.
      [1913 Webster]

   7. A stone, commonly flat, used to sharpen cutting tools; a
      whetstone; -- called also rubstone.
      [1913 Webster]

   Rub iron, an iron guard on a wagon body, against which a
      wheel rubs when cramped too much.

   Rub of the green (Golf), anything happening to a ball in
      motion, such as its being deflected or stopped by any
      agency outside the match, or by the fore caddie.
      [1913 Webster + Webster 1913 Suppl.]

The Collaborative International Dictionary of English v.0.48:

Rub \Rub\, v. i.
   1. To move along the surface of a body with pressure; to
      grate; as, a wheel rubs against the gatepost.
      [1913 Webster]

   2. To fret; to chafe; as, to rub upon a sore.
      [1913 Webster]

   3. To move or pass with difficulty; as, to rub through woods,
      as huntsmen; to rub through the world.
      [1913 Webster]

   To rub along or on, to go on with difficulty; as, they
      manage, with strict economy, to rub along. [Colloq.]
      [1913 Webster]

WordNet (r) 3.0 (2006):

rub
    n 1: an unforeseen obstacle [syn: hang-up, hitch, rub,
         snag]
    2: the act of rubbing or wiping; "he gave the hood a quick rub"
       [syn: rub, wipe]
    v 1: move over something with pressure; "rub my hands"; "rub oil
         into her skin"
    2: cause friction; "my sweater scratches" [syn: rub, fray,
       fret, chafe, scratch]
    3: scrape or rub as if to relieve itching; "Don't scratch your
       insect bites!" [syn: rub, scratch, itch]

Moby Thesaurus II by Grady Ward, 1.0:

315 Moby Thesaurus words for "rub":
   Discordia, Eris, ablate, abrade, abrase, afflict, aggravate,
   agonize, ail, air-dry, anhydrate, annoy, apple of discord,
   attouchement, bake, bandage, bar, bark, bathe, bite, block,
   blockade, blot, bone of contention, bone to pick, bother,
   bottleneck, breath, brush, brush by, buff, burn, burnish, care for,
   caress, casus belli, catch, catch a likeness, chafe, character,
   characterize, chart, clash, clashing, climacteric, clutch,
   come in contact, conflict, confrication, contact, contention,
   contingence, convergence of events, convulse, cordon, crimp,
   crisis, critical juncture, critical point, crossroads,
   crow to pick, crow to pluck, crucial period, crucify, crunch, crux,
   cure, curtain, cut, cutaneous sense, dehumidify, dehydrate,
   delineate, depict, desiccate, determent, deterrent, diagnose,
   diagram, difficulty, disaccord, disaffinity, discord, discordance,
   discordancy, disharmony, distress, doctor, drain, draw, drawback,
   dry, emergency, enmity, erase, erode, evaporate, exasperate,
   excoriate, excruciate, exigency, exsiccate, extremity, feel,
   feel up, feeling, fester, file, fingertip caress, finish, fire,
   flick, flux, fondle, fray, frazzle, fret, frication, friction,
   frictionize, frottage, furbish, gall, give care to, give pain,
   glance, glaze, gloss, gnaw, gnaw away, grate, graze, grind, gripe,
   grounds for war, hamper, hand-mindedness, hang-up, harrow, hazard,
   heal, hinge, hit, hit off, hitch, hurdle, hurt, impediment,
   impinge, impingement, impingence, incompatibility,
   incompatibleness, inflame, inflict pain, inharmoniousness,
   inharmony, insolate, irk, irritate, jangle, jar, joker,
   kill by inches, kiln, kiss, knead, lacerate, lambency, lap, lick,
   light touch, limn, luster, map, martyr, martyrize, massage,
   minister to, mischief, mummify, nettle, nip, noncooperation, nose,
   notate, nudge, nurse, nuzzle, objection, obstacle, obstruction,
   obstructive, one small difficulty, open conflict, operate on,
   osculate, osculation, pain, paint, parch, pass, peeve,
   perfrication, pet, physic, picture, picturize, pierce, pinch,
   plaster, polish, portray, poultice, prick, print,
   prolong the agony, provoke, purge, push, put to torture, rack,
   rankle, rasp, raze, register, remedy, render, represent, rile,
   rub against, rub away, rub down, rub noses, rub off, rub out,
   rubbing, ruffle, schematize, scorch, scour, scrape, scrub, scuff,
   sear, sense of touch, shave, shine, shrivel, sideswipe, skim, skin,
   skirt, sleek, slick, slick down, smoke, snag, soak up, sore point,
   splint, sponge, squeak by, stab, sting, strained relations, strait,
   strap, stroke, stumbling block, stumbling stone, sun, sun-dry,
   swab, symbolize, tactile sense, taction, take a rubbing, tangency,
   tap, tender spot, tension, tentative contact, tentative poke,
   ticklish issue, torment, torrefy, torture, touch, touching, towel,
   trace, trace out, trace over, traverse, treat, turn, turning point,
   tweak, twist, unharmoniousness, unpleasantness, varnish, vex, wax,
   wear, wear away, weazen, whisper, wipe, wither, wizen, wound,
   wring, write