Source : Webster's Revised Unabridged Dictionary (1913)

Unbend \Un*bend"\, v. t. [imp. & p. p. {Unbent}; 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.

   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.

            You do unbend your noble strength.    --Shak.

   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.

Unbend \Un*bend"\, v. i.
   1. To cease to be bent; to become straight or relaxed.

   2. To relax in exertion, attention, severity, or the like;
      hence, to indulge in mirth or amusement.

Source : WordNet®

unbend
     v 1: straighten up or out; make straight [syn: {straighten}]
          [ant: {bend}]
     2: unfasten, as a sail, from a spar or a stay
     3: free from flexure; "unbend a bow" [ant: {flex}]
     4: make less tight; "relax the tension on the rope" [syn: {relax}]
     5: become less tense, rest, or take one's ease; "He relaxed in
        the hot tub"; "Let's all relax after a hard day's work"
        [syn: {relax}, {loosen up}, {unwind}, {decompress}, {slow
        down}] [ant: {tense}]
     6: release from mental strain, tension, or formality; "unbend
        the mind from absorbing too much information"
     [also: {unbent}]