Brewer:
Usher means a porter. (Old French, muisher, a door; whence huissier, an usher; Latin, ostiarius.) One who
stands at the door to usher visitors into the presence. (Scotch, Wishart.)
And ostiarium is from ostium=door, from os, oris = mouth. Remember Ostium, port of Rome, was
at the mouth of the Tiber.