Green’s Dictionary of Slang

(US) a ‘torch’ singer, a singer of maudlin, romantic songs.

1940		R. Chandler Farewell, My Lovely (1949) 250: A handsome black-haired, black-browed torcher who could sing as if she meant it.
1951		Green & Laurie Show Biz from Vaude to Video 572: Torcher – torch singer.
1959		J. Blake letter 10 Mar. in Joint (1972) 130: Had a little help from, of all chronic torchers, Lady Day.