The Collaborative International Dictionary of English v.0.48:

Phosphinic \Phos*phin"ic\ (f[o^]s*f[i^]n"[i^]k), a. (Chem.)
   Pertaining to, or designating, certain acids analogous to the
   phosphonic acids, but containing two hydrocarbon radicals,
   and derived from the secondary phosphines by oxidation.
   [1913 Webster]