One theory says this practice came from knights lifting their visors when greeting a friend
: 
But ... During the days of chivalry, knights often wore full armor in public, and 
usually ... To open a visor was a form of greeting which said in effect: "I do not 
expect a ... Moderns remove the hat as a sign of respect in greeting a friend, 
always when... [DOC] [TLE] September XX, 2008 [PAR] What unit of measure is equal to one eighth of a mile?