五日

1. Origins, structure, and basic meaning

• Structure: 五日, read いつか, means either a span of five days or the fifth day of a month.
• Basic usage: 五日が過ぎた counts elapsed time; 今月の五日に identifies a calendar date.

2. Common pitfalls and similar expressions

• Five-day duration and fifth-day date
  • 過ぎた selects duration, whereas 今月の...に selects the date; both share the reading いつか.