whole day and night; 24 hours
Refers to a continuous period of one full day and night. Often used in contexts like travel, work, or duration.
It took a whole day and night to reach the destination.
This work cannot be finished in 24 hours.
Compound of 一 (one), 昼 (daytime), and 夜 (night). The reading いっちゅうや follows regular sound changes.