(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

参加: participation / 酸化: oxidation, combustion / 惨禍: catastrophe, disaster / 傘下: subsidiary / 産科: obstetrics / 賛歌, 讃歌, 讚歌: song of praise, hymn, paean / 山家: mountain villa

酸化: oxidize, become oxidized / 参加: participate, join, take part

A title used after person's name (first name or surname) regardless of sex; Mr, Ms, Mrs, Miss. Also used after a job title and a company name. / (colloquial) Used after a shop name.

三角形: triangle

三月, 3月: March

三人: three people

三男: third son; three men