adjective.
Of, relating to, or containing phosphorus, especially with valence 3 or a valence lower than that of a comparable phosphoric compound.
The Century Dictionary and Cyclopedia
Pertaining to, obtained from, or containing phosphorus.
the GNU version of the Collaborative International Dictionary of English
adjective.
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.