Source : Webster's Revised Unabridged Dictionary (1913)

Manganous \Man"ga*nous\, a. (Chem.)
   Of, pertaining to, designating, those compounds of manganese
   in which the element has a lower valence as contrasted with
   manganic compounds; as, manganous oxide.

   {Manganous acid}, a hypothetical compound analogous to
      sulphurous acid, and forming the so-called manganites.