Song, Composing A Poem Or Song
A composed song is a poem, or a song. This can also refer to the act of composing a poem or song, which makes a lot of sense given the kanji.
This is used particularly when referring to waka poetry.
This is a jukugo word that uses the on'yomi for both kanji. You should be able to read this on your own.
Everyone, do you know who wrote this poem?
Just before he was assassinated, he had written a poem.
Chanting Buddhist teachings in the form of a waka poem with a melody is called "goeika".