If you describe a person or their behaviour as ~, you mean that they have very strict beliefs and attitudes, which they are unwilling to change.
He was rigid and ~.
...her ~ opposition to the old regime.
= inflexible
ADJ
UNBENDING
Meaning of UNBENDING in English
Collins COBUILD. Толковый словарь английского языка для изучающих язык Коллинз COBUILD (международная база данных языков Бирмингемского университета) . 2012