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]