noun, na-adjective
strong determination; strong-willed; firmness of purpose
Describes a person or attitude marked by unwavering resolve and firm will. Often used in formal or written contexts.
彼は意志堅固な人で、一度決めたことは最後までやり遂げる。
He is a strong-willed person who sees through whatever he decides.
意志堅固であれば、どんな困難も乗り越えられる。
With firm determination, you can overcome any difficulty.
Yojijukugo composed of 意志 (will, intention) and 堅固 (firm, solid). The combination directly conveys an unyielding will.