1) knot or band by which two things are fastened together, to
    fasten or gird one's self

 This was the white scarf or apron of slaves, which was fastened to
 the belt of the vest and distinguished slaves from freemen, hence in
 1 Pet. 5:5, "gird yourselves with humility as your servile garb"
 means by putting on humility, show your subjection one to another.
 Also, this refers to the overalls which slaves wore to keep clean
 while working, an exceedingly humble garment.