exordium

exordium \ig-ZAWR-dee-uhm\, noun:

1. The beginning of anything.
2. The introductory part of an oration, treatise, etc.

As for your beginning and exordium, I no longer remember it, nor consequently the middle; and as for your conclusion, I will do nothing of the sort.
-- Michel de Montaigne, "Of the Education of Children," Essays

In commencing, with the New Year, a New Volume, we shall be permitted to say a very few words by way of exordium to our usual chapter of Reviews, or, as we should prefer calling them, of Critical Notices.
-- Edgar Allan Poe, "Literary Criticism," The Complete Works of Edgar Allan Poe, Vol. 11

Exordium stems from the Latin root ōrd meaning "to begin." The prefix ex- in this case means "utterly," and the suffix -ium which is often found on nouns borrowed from Latin, such as delirium and tedium.