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).
We must solve this problem as soon as possible.
It's a situation where every moment counts.
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.
He has a stubborn personality and doesn't listen to others' opinions.
He studied hard, not wanting to waste a single moment.
My grandfather is a stubborn person who never changes his opinion.