also: にちがい
adverb
at one time; once; some time ago
Rare literary adverb meaning 'once' or 'formerly'. Not used in modern everyday speech; encountered mainly in older texts.
日外、この地に大きな城があったという。
Once, there was said to have been a large castle in this area.
The historical derivation is uncertain; the kanji 日 (day) and 外 (outside) may suggest a meaning like 'outside of (recent) days', i.e., 'in the past'.