The Collaborative International Dictionary of English v.0.48:

Unbend \Un*bend"\ ([u^]n*b[e^]nd"), v. t. [imp. & p. p. Unbent
   ([u^]n*b[e^]nt"); p. pr. & vb. n. Unbending.] [1st pref.
   un- + bend.]
   1. To free from flexure; to make, or allow to become,
      straight; to loosen; as, to unbend a bow.
      [1913 Webster]

   2. A remit from a strain or from exertion; to set at ease for
      a time; to relax; as, to unbend the mind from study or
      care.
      [1913 Webster]

            You do unbend your noble strength.    --Shak.
      [1913 Webster]

   3. (Naut.)
      (a) To unfasten, as sails, from the spars or stays to
          which they are attached for use.
      (b) To cast loose or untie, as a rope.
          [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Unbending \Un*bend"ing\, a. [In senses 1, 2, and 3, pref. un-
   not + bending; in sense 4, properly p. pr. of unbend.]
   1. Not bending; not suffering flexure; not yielding to
      pressure; stiff; -- applied to material things.
      [1913 Webster]

            Flies o'er the unbending corn, and skims along the
            main.                                 --Pope.
      [1913 Webster]

   2. Unyielding in will; not subject to persuasion or
      influence; inflexible; resolute; -- applied to persons.
      [1913 Webster]

   3. Unyielding in nature; unchangeable; fixed; -- applied to
      abstract ideas; as, unbending truths.
      [1913 Webster]

   4. Devoted to relaxation or amusement. [R.]
      [1913 Webster]

            It may entertain your lordships at an unbending
            hour.                                 --Rowe.
      [1913 Webster] -- Un*bend"ing*ly, adv. --
      Un*bend"ing*ness, n.
      [1913 Webster]

WordNet (r) 3.0 (2006):

unbending
    adj 1: incapable of adapting or changing to meet circumstances;
           "a rigid disciplinarian"; "an inflexible law"; "an
           unbending will to dominate" [syn: inflexible, rigid,
           unbending]

Moby Thesaurus II by Grady Ward, 1.0:

127 Moby Thesaurus words for "unbending":
   adamant, adamantine, aloof, arrowlike, cast-iron, constant,
   dead straight, direct, distant, dour, even, firm, fixed, flat,
   flinty, fundamentalist, grim, hard, hard-core, hidebound,
   horizontal, immovable, immutable, implacable, impliable, in a line,
   inductile, inelastic, inexorable, inextensible, inextensile,
   inextensional, inflexible, insociable, intractable, intractile,
   intransigent, iron, ironbound, ironclad, ironhanded,
   irreconcilable, irresilient, level, lineal, linear, loyal,
   muscle-bound, nonelastic, nonstretchable, obdurate, obstinate,
   offish, orthodox, procrustean, purist, puristic, puritan,
   puritanic, rectilineal, rectilinear, relentless, reserved, right,
   rigid, rigorist, rigoristic, rigorous, rock-ribbed, rockbound,
   ruler-straight, set, settled, single-minded, smooth, sot,
   standoffish, staunch, steadfast, steady, steely, stern, stiff,
   straight, straight-cut, straight-front, straight-side,
   straightlaced, straitlaced, streamlined, stubborn, true,
   unaffected, unalterable, unapproachable, unbent, unbowed, unbroken,
   unchangeable, uncommunicative, uncompromising, uncurved,
   undeflectable, undeflected, undeviating, undistorted, unextendible,
   unextensible, unflappable, unflexible, ungiving, uninterrupted,
   unlimber, unmalleable, unmoved, unpliable, unpliant, unrelenting,
   unshaken, unswayable, unswerving, untractable, unturned,
   unyielding, upright, vertical, withdrawn