noun
a moment; an instant; a short time
Refers to a very brief period of time, often used in set phrases like 一刻も早く (as soon as possible).
一刻も早くこの問題を解決しなければならない。
We must solve this problem as soon as possible.
It's a situation where every moment counts.
na-adjective
Dated term for a stubborn or inflexible person. It was also written as 一国, 一克, or 一剋, but 一刻 is the standard kanji form.
彼は一刻な性格で、人の意見を聞かない。
He has a stubborn personality and doesn't listen to others' opinions.