Sentence:  A close helmet entirely covers the head, face, and neck, having on the front perforations for the admission of air, and slits through which the wearer may see objects around him, this part which is stiled the <WSD>visor</WSD> lifts up by means of a pivot over each ear. 
Meaning of the word marked with <WSD> tags:  A part of a helmet, arranged so as to lift or open, and so show the face. The openings for seeing and breathing are generally in it.