Source : Webster's Revised Unabridged Dictionary (1913)

Phosphorous \Phos"phor*ous\, a. [Cf. F. phosphoreux.] (Chem.)
   Of or pertaining to phosphorus; resembling or containing
   phosphorus; specifically, designating those compounds in
   which phosphorus has a lower valence as contrasted with
   phosphoric compounds; as, phosphorous acid, {H3PO3}.