historic, historical / already-happened, past / former, old, traditional

historian

study of history

(Internet slang, especially anime and manga fandom) events or things from the past which one wants to whitewash/erase from history (due to it being embarrassing, poorly received, etc.); dark past

oral history

historicism

once in a lifetime

the emperor's residence, the imperial palace / the capital, especially within an empire

(historical) (Japanese colonial era) Seoul, also known as Gyeongseong (the Korean reading of these same Chinese characters) and Keijō

(obsolete) the emperor's residence, the imperial palace / (obsolete) the capital, especially within an empire