Definition of "vizor"

He was a big man and looked terrifying in his armour and facelessness because of the helmet and vizor.

1966, James Workman, The Mad Emperor, Melbourne, Sydney: Scripts, page 71

Heavy helmet with vizor of polished iron ...

2004, Wolfgang Bruhn, Max Tilke, A Pictorial History of Costume From Ancient Times to the Nineteenth Century‎, Courier Dover Publications, page 25