To free from flexure; to make, or allow to become, straight; to loosen; as, to unbend a bow
If someone unbends, their attitude becomes less strict than it was. In her dying days the old Queen unbent a little. unbent to relax and start behaving in a less formal way
To relax in exertion, attention, severity, or the like; hence, to indulge in mirth or amusement
release from mental strain, tension, or formality; "unbend the mind from absorbing too much information" free from flexure; "unbend a bow" unfasten, as a sail, from a spar or a stay