1. (n.)manganese a hard, brittle, grayish white, metallic element, an oxide of which, MnO
Etymology: (1670–80; < F manganèse < It manganese manganese dioxide, of obscure origin)
Definition of 'manganese'
Princeton's WordNet
1. (noun)manganese, Mn, atomic number 25 a hard brittlegrey polyvalent metallicelement that resembles iron but is not magnetic; used in making steel; occurs in many minerals
Definition of 'manganese'
Webster Dictionary
1. (noun)manganese an element obtained by reduction of its oxide, as a hard, grayish white metal, fusible with difficulty, but easily oxidized. Its ores occur abundantly in nature as the minerals pyrolusite, manganite, etc. Symbol Mn. Atomic weight 54.8
Definitions of manganese 
