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.

Source: Webster's Revised Unabridged Dictionary (1913)