unbend (v.)
mid-13c., "relax a bow by unstringing it," from un- (2) "reverse, opposite of" + bend (v.). Intransitive sense from 1746. Figurative meaning "to become genial, relax" (1748) has a sense opposite to that of unbending "inflexible, obstinate" (1680s), which does not derive from the bow-stringing image.