一昨日(いっさくじつ)

いっさくじつ is the formal reading of 一昨日(おととい) (the day before yesterday). Both use the same kanji but differ in register.

Reading contrast

• おととい: everyday conversation, casual speech
• いっさくじつ: news broadcasts, official documents, formal writing, business contexts

Common patterns

The 一昨(いっさく)〜 prefix means "the ~ before last" and applies to other time words:

• 一昨日(いっさくじつ): the day before yesterday
• 一昨年(いっさくねん): the year before last
• 一昨晩(いっさくばん): the night before last

Similar time words

• 昨日(きのう)/昨日(さくじつ): yesterday (casual/formal)
• 明後日(あさって)/明後日(みょうごにち): the day after tomorrow (casual/formal)