From Longman Dictionary of Contemporary Englishunbendun‧bend /ʌnˈbend/ verb (past tense and past participle unbent /-ˈbent/) [intransitive]RELAXED to relax and start behaving in a less formal way→ See Verb table
Examples from the Corpus
unbend• Even Isay unbent a little, and grinned at a raven-haired wench when she made a lewd pluck at his staff.• If only he could unbend and relax, even give a genuine smile or make a pleasantry.• She unbent enough to ask us in for something to eat. 