Fundamental Synonyms

Basic, rudimentary, elementary, basal, root, cardinal, original, first, primordial, chief, key, structural, constitutional, intrinsic, vital, important, necessary, pivotal, foundational, elemental, underlying, radical, primary, initial, prime, primitive, principal, capital, central, organic, inherent, ingrained, essential, indispensable, crucial, and critical.

Basics, rudiments, basic principles, preliminaries, essence, nucleus, base, groundwork, heart of the matter, nuts and bolts, brass tacks, essentials, foundations, first principles, crux, core, heart, bedrock, crux of the matter, sine qua non, nitty-gritty, and ABC.