noun
Historical term for a person highly skilled in a particular art, profession, or trade. Now rare; modern Japanese would use 達人, 名人, or 専門家.
江戸時代の文献には、剣術の其れ者として名を残す者がいる。
In Edo-period documents, there are those who are remembered as masters of swordsmanship.
noun
Historical euphemism for a geisha or prostitute, used in the pleasure quarters. Now archaic; modern terms are 芸者 or 遊女.
其れ者は、かつて花街で芸を披露した女性を指した。
其れ者 once referred to women who performed arts in the red-light district.
From 其れ (that) + 者 (person), literally 'that person', used euphemistically to refer to an expert or a geisha/prostitute in historical contexts. The exact derivation is uncertain.