Source : Webster's Revised Unabridged Dictionary (1913)

Exordium \Ex*or"di*um\ (-[u^]m), n.; pl. E. {Exordiums}
   (-[u^]mz), L. {Exordia} (-[.a]). [L. fr. exordiri to begin a
   web, lay a warp, begin; ex out + ordiri to begin a web,
   begin; akin to E. order. See {Order}.]
   A beginning; an introduction; especially, the introductory
   part of a discourse or written composition, which prepares
   the audience for the main subject; the opening part of an
   oration. ``The exordium of repentance.'' --Jer. Taylor.
   ``Long prefaces and exordiums. '' --Addison.

Source : WordNet®

exordium
     n : (rhetoric) the introductory section of an oration or
         discourse
     [also: {exordia} (pl)]