The Collaborative International Dictionary of English v.0.48:

Usher \Ush"er\, n. [OE. ussher, uschere, OF. ussier, uisser,
   oissier, hussier, huissier, fr. L. ostiarius a doorkeeper,
   fr. ostium a door, entrance, fr. os mouth. See Oral, and
   cf. Ostiary.]
   [1913 Webster]
   1. An officer or servant who has the care of the door of a
      court, hall, chamber, or the like; hence, an officer whose
      business it is to introduce strangers, or to walk before a
      person of rank. Also, one who escorts persons to seats in
      a church, theater, etc. "The ushers and the squires."
      --Chaucer.
      [1913 Webster]

            These are the ushers of Marcius.      --Shak.
      [1913 Webster]

   Note: There are various officers of this kind attached to the
         royal household in England, including the gentleman
         usher of the black rod, who attends in the House of
         Peers during the sessions of Parliament, and twelve or
         more gentlemen ushers. See Black rod.
         [1913 Webster]

   2. An under teacher, or assistant master, in a school.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Usher \Ush"er\, v. t. [imp. & p. p. Ushered; p. pr. & vb. n.
   Ushering.]
   To introduce or escort, as an usher, forerunner, or
   harbinger; to forerun; -- sometimes followed by in or forth;
   as, to usher in a stranger; to usher forth the guests; to
   usher a visitor into the room.
   [1913 Webster]

         The stars that usher evening rose.       --Milton.
   [1913 Webster]

         The Examiner was ushered into the world by a letter,
         setting forth the great genius of the author.
                                                  --Addison.
   [1913 Webster]

WordNet (r) 3.0 (2006):

Usher
    n 1: Irish prelate who deduced from the Bible that Creation
         occurred in the year 4004 BC (1581-1656) [syn: Ussher,
         James Ussher, Usher, James Usher]
    2: an official stationed at the entrance of a courtroom or
       legislative chamber [syn: usher, doorkeeper]
    3: someone employed to conduct others [syn: usher, guide]
    v 1: take (someone) to their seats, as in theaters or
         auditoriums; "The usher showed us to our seats" [syn:
         usher, show]

Moby Thesaurus II by Grady Ward, 1.0:

103 Moby Thesaurus words for "usher":
   Ganymede, Hebe, MC, airline hostess, airline stewardess, attend,
   attendant, auteur, ballyhoo man, barker, batman, bellboy, bellhop,
   bellman, best man, bodyguard, bootblack, boots, bridemaiden,
   bridesmaid, bridesman, cabin boy, caddie, callboy, cavalier,
   cerberus, chaperon, chore boy, companion, concierge, conduct,
   conductor, convoy, copyboy, costume designer, costumer, costumier,
   cupbearer, director, doorkeeper, doorman, duenna, emcee,
   equestrian director, errand boy, errand girl, escort, esquire,
   exhibitor, fellow traveler, footboy, gatekeeper, gofer, groomsman,
   guard, guide, hostess, impresario, introduce, janitor, lead,
   makeup man, marshal, master of ceremonies, matron of honor,
   office boy, office girl, orderly, ostiary, page, paranymph,
   playreader, porter, preface, producer, prompter, receptionist,
   ringmaster, safe-conduct, scenewright, set designer, shepherd,
   showman, spieler, squire, stage director, stage manager, steward,
   stewardess, swain, take out, tender, theater man, theatrician,
   ticket collector, trainbearer, usherer, usherette, wait on, warden,
   wedding attendant, wedding party, yeoman



Bouvier's Law Dictionary, Revised 6th Ed (1856):

USHER. This word is said to be derived from a huissier, and is the name of
an inferior officer in some English courts of law Archb. Pr. 25.