principia
First principles; elementary material.
archaic
I do really think, that your book […] might become an institute, containing the principia of those laws of motion, by which the system of the human community is framed and doth act […]
1776, Thomas Pownall, in a letter to the economist Adam Smith
Where it comes from
Learned borrowing from Latin prī̆ncipia.
Adapted from the Wiktionary entry principia (CC BY-SA 4.0).