original song
Refers to the original version of a song, as opposed to a cover, remix, or parody.
The original song for this piece is a 1970s folk song.
カバーより元歌のほうが好きだ。
I prefer the original song to the cover.
Compound of 元 (moto, 'origin') and 歌 (uta, 'song'). The reading もとうた is a straightforward kun'yomi combination.