a while, a period of time

importance

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

period drama

a historical period where social disorder is so great due to war, disease, political disorder etc. that there is little or no cultural development; Dark Ages