This involuntary separation helped the brothers form a bond that has proven to be unyielding and unmatched.
en.wikipedia.org She disliked the disciplines imposed by an unsympathetic and unyielding superior, and she stayed only a few months.
en.wikipedia.org Described as having been a frivolous and high-spirited princess, she also, at an early age, had displayed a tendency to be both stubborn and unyielding.
en.wikipedia.org Used as an adjective and sometimes as a noun, it refers to something stern, harsh, unyielding, inflexible, rigid, sturdy, strong, robust.
en.wikipedia.org Unyielding and always full of confidence, he confronts anything without hesitation to fight right away.
en.wikipedia.org