A phosphite in inorganic chemistry is a salt of phosphorous acid, H3PO3 and following the IUPAC naming recommendations the phosphite ion would be PO33− a salt of P(OH)3. Historically phosphite has referred to salts containing HPO32− and this is because aqueous H3PO3 is not triprotic P(OH)3 but almost exclusively the diprotic HP(O)(OH)2 (IUPAC ...
• (n.) A salt of phosphorous acid.
Phos'phite noun (Chemistry) A salt of phosphorous acid. 
Type: Term Pronunciation: fos′fīt Definitions: 1. A salt of phosphorous acid.
phosphite Any salt or ester of phosphorous acid.