《Etenraku》

...It is also written as Fuuki, Fuuki, and Fuuki. It is also called "Etenraku (the song)". It is the most classical piece that shows the process by which "Etenraku Utaimono" with koto accompaniment developed into songs in the form of a group song.

*Some of the terminology explanations that mention "Koshitenraku" are listed below.

Source | Heibonsha World Encyclopedia 2nd Edition | Information

…富貴，蕗，布貴などとも書く。《越天楽(の曲)》ともいう。箏伴奏の〈越天楽歌物（うたいもの）〉が組歌形式の歌曲に発展した過程を示すものの最古典曲。…

※「《越天楽》」について言及している用語解説の一部を掲載しています。

出典｜株式会社平凡社世界大百科事典 第２版について | 情報