iut comes from the ancient egyptians when they were in great camel trains, pushing ,yelling and shouting and camels trying to wander off not going where they needed too, the drivers went to the riverside and pulled a rush out of the rushes with which they beat wayward camels into line, which although VERY SLOW during that hour before the gates closed was usually successful and became known as the RUSH hour.. . If you believe that well !!!!!