一日中

1. Origins, structure, and basic meaning

• Structure: Written 一日中 and read いちにちじゅう, it means throughout virtually the whole day, from morning into evening.
• Basic usage: It appears with rain preventing an outing and a holiday spent reading at home.

2. Common pitfalls and similar expressions

• Not necessarily an exact twenty-four hours
  • Everyday use emphasizes the entire practical day rather than a strict midnight-to-midnight interval.