noun, noun which may take the genitive case particle 'no'
tenacity; indomitability; unyielding spirit
A yojijukugo describing a strong will that never bends or breaks, used in formal or literary contexts to praise perseverance.
彼の不撓不屈の精神が、ついに難病を克服させた。
His indomitable spirit finally enabled him to overcome the serious illness.
不撓不屈の努力で目標を達成した。
Through tenacious effort, he achieved his goal.