one previous; the one before last
Rare standalone noun meaning 'the one before last', typically used in temporal expressions such as 一昨年 (the year before last) or 一昨日 (the day before yesterday). In modern Japanese, it is almost always part of a compound rather than used independently.
The word 一昨 is rarely used alone; it appears in forms like 一昨年 (the year before last) and 一昨日 (the day before yesterday).
two days before yesterday; three days ago
the night before last
three ... ago; two ... before last
night before last
two nights before last
Compound of 一 (one) and 昨 (previous), literally 'one previous'. The standalone use is rare; it mainly serves as a bound element in temporal nouns.