終日

1. Origins, structure, and basic meaning

• Structure: 終日 is read as しゅうじつ and is a time noun or adverb meaning throughout the entire day.
• Basic usage: A continuing state appears in 終日にぎわう, while all-day suspension appears in 終日欠航.

2. Common pitfalls and similar expressions

• Difference from 一日中
  • The meanings overlap, but 終日 is compact and formal, fitting notices, reports, and business contexts.
• The whole relevant day
  • It indicates continuation across the day or operating period rather than only part of it.