fundamental
n. countablen. a basic rule, fact, or skill that you must learn first because everything else depends on it.
n. a central or primary rule, principle, or law on which something is based. Often used in the plural to describe the essential components of a system or discipline.
You need to learn the fundamentals of math before taking this class.
The coach spent the first week of training focusing on the fundamentals of footwork and balance.
While the technology has evolved rapidly, the fundamentals of human communication remain rooted in empathy and active listening.
From Late Latin fundamentālis, from Latin fundamentum (“foundation”), from fundō (“to lay the foundation (of something), to found”), from fundus (“bottom”), from Proto-Indo-European *bʰudʰmḗn.
Frequently used in the plural form ('fundamentals') when referring to the basic principles of a subject.