verb (v)

• straighten up or out; make straight(verb.motion)

  Synonym:
  straighten
  Antonym:
  bend, flex
  

  source: wordnet30
• unfasten, as a sail, from a spar or a stay(verb.contact)

  source: wordnet30
• free from flexure(verb.contact)

  Example:
  Unbend a bow.
  

  Antonym:
  bend, deform, flex, turn, twist
  

  source: wordnet30
• make less taut(verb.change)

  Synonym:
  relax
  

  source: wordnet30
• become less tense, rest, or take one's ease(verb.body)

  Synonym:
  decompress, loosen up, relax, slow down, unwind
  Antonym:
  tense, tense up
  

  source: wordnet30
• release from mental strain, tension, or formality(verb.body)

  Example:
  Unbend the mind from absorbing too much information.
  

  source: wordnet30
• To free from flexure; to make, or allow to become, straight; to loosen; as, to unbend a bow.(verb)

  source: webster1913
• To cease to be bent; to become straight or relaxed.(verb)

  source: webster1913