The Collaborative International Dictionary of English v.0.48:

Rankle \Ran"kle\ (r[a^][ng]"k'l), v. t.
   To cause to fester; to make sore; to inflame. [R.] --Beau. &
   Fl.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Rankle \Ran"kle\ (r[a^][ng]"k'l), v. i. [imp. & p. p. Rankled
   (-k'ld); p. pr. & vb. n. Rankling (-kl[i^]ng).] [From
   Rank, a.]
   1. To become, or be, rank; to grow rank or strong; to be
      inflamed; to fester; -- used literally and figuratively.
      [1913 Webster]

            A malady that burns and rankles inward. --Rowe.
      [1913 Webster]

            This would have left a rankling wound in the hearts
            of the people.                        --Burke.
      [1913 Webster]

   2. To produce a festering or inflamed effect; to cause a
      sore; -- used literally and figuratively; as, a splinter
      rankles in the flesh; the words rankled in his bosom.
      [1913 Webster]

WordNet (r) 3.0 (2006):

rankle
    v 1: gnaw into; make resentful or angry; "The injustice rankled
         her"; "his resentment festered" [syn: eat into, fret,
         rankle, grate]

Moby Thesaurus II by Grady Ward, 1.0:

108 Moby Thesaurus words for "rankle":
   afflict, aggravate, agonize, ail, anger, annoy, arouse,
   be remembered, bite, bother, break up, bristle, burn, canker,
   chafe, convulse, corrupt, crucify, crumble, crumble into dust, cut,
   decay, decompose, disintegrate, distress, embitter, exasperate,
   excruciate, fall into decay, fall to pieces, fester, fret, gall,
   gangrene, get to, give pain, gnaw, go bad, go to pieces, grate,
   grind, gripe, harass, harrow, huff, hurt, incense, inflame,
   inflict pain, irk, irritate, kill by inches, lacerate,
   make an impression, martyr, martyrize, matter, miff, mildew, mold,
   molder, mortify, necrose, nettle, never be forgotten, nip, obsess,
   pain, peeve, penetrate, pierce, pinch, pique, plague, prick,
   prolong the agony, provoke, put to torture, putrefy, putresce,
   rack, rasp, rile, ripen, roil, rot, rub, ruffle, run, set up,
   sink in, sphacelate, spoil, stab, sting, stir the blood, stir up,
   suppurate, torment, torture, tweak, twist, upset, vex, weep,
   work up, wound, wring