belt out

Reader's　Digest 7/8月合併号の記事 "A Song in His Heart" からの引用です。

At a medical laboratory clinic in Waterloo, Ontario, an elderly woman sat on the edge of a waiting room chair belting out the Celine Dion tune "My Heart Will Go On."

"belting out" は歌うことだと文脈から推測できますが、辞書で "belt" を見てもその様な意味は出てきません。しかし、"belt out" で次の様に説明がありました。

・Macmillan Dictionary: shout or sing something loudly, or to play something loudly on a musical instrument: Mahalia Jackson belting out a gospel tune

・Collins Dictionary: If you belt out a song, you sing or play it very loudly.
[informal]: We shouldn't have opera singers belting out the national anthem before England matches.

・Wiktionary: to sing loudly; to emit music loudly: He belted out Sweet Child of Mine at the karaoke.