〜に一回

1. Origins, structure, and basic meaning

• Structure: Put に after the reference period and state the number of occurrences within it. 一回 is read いっかい.
• Basic usage: It expresses the frequency of a recurring action.
  • 週に一回、図書館へ行きます。 gives the frequency of going to the library once each week.

2. Common pitfalls and similar expressions

• Period and length of one occurrence
  • 週に一回 gives a frequency, while 一回に一時間 gives the time spent on each occasion. Distinguish occurrences per period from the duration of one occurrence.
• Relation to 一度
  • For recurring frequency, both 月に一度 and 月に一回 mean once a month. 一度 is read いちど here.
• Distinct from a calendar time
  • 月曜日に行く specifies the day of the week, while 週に二回行く specifies the number of visits each week. Frequency alone does not determine the particular days.