Source : Webster's Revised Unabridged Dictionary (1913)

Manganate \Man"ga*nate\, n. [Cf. F. manganate.] (Chem.)
   A salt of manganic acid.

   Note: The manganates are usually green, and are wellknown
         compounds, though derived from a hypothetical acid.

Source : WordNet®

manganate
     n : a salt of manganic acid containing manganese as its anion