noun
stubborn person; obstinate person
Describes a person who is inflexible, headstrong, or set in their ways. Often carries a negative or critical tone.
彼は一刻者だから、一度決めたら絶対に曲げない。
He's so stubborn that once he decides something, he never backs down.
It's impossible to persuade that obstinate person.
The exact derivation is uncertain. 一刻 (いっこく) can mean 'stubborn' or 'short-tempered', and 者 (もの) means 'person'. The kanji 一国者 is a rare variant, possibly ateji.