hypophosphoric

Century Dictionary and Cyclopedia

1. Same as hypophosphorous.
2. Noting an acid, a distinct tetra basic acid, H₄P₂O₆, produced, along with phosphorous and phosphoric acids, by the slow oxidation of phosphorus in moist air at ordinary temperatures.

Wiktionary

1. adj. Of or pertaining to hypophosphoric acid or its derivatives

GNU Webster's 1913

1. adj. Pertaining to, or derived from, or containing, phosphorus in a lower state of oxidation than in phosphoric compounds.