noun, noun or participle which takes 'suru'
strenuous effort; diligent work enduring hardships
A yojijukugo describing intense, persevering effort in the face of difficulty. Often used in formal or literary contexts to praise dedication.
彼は刻苦精進の末、ついに難関試験に合格した。
After strenuous effort, he finally passed the difficult exam.
Polish one's skills through diligent work and hardship.