sodium hydrosulfite

noun, Chemistry
1.
a white, crystalline, water-soluble powder, Na 2 S 2 O 4 , used as a reducing agent, especially in dyeing, and as a bleach.
Also called hydrosulfite, sodium dithionite
[dahy-thahy-uh-nahyt] /daɪˈθaɪ əˌnaɪt/ (Show IPA),
sodium hyposulfite.