adequacy, basal, basis, cardinal, consistency, constant, constituent, content, cornerstone, crucial, crux, elementary, essence, essential, facet, foundational, fundamental, hardwired, holistic, immutable, imperative, indispensable, inevitable, inexorable, inherent, integral, intrinsic, irreducible, kernel, livelihood, mainstay, outright, pivotal, prerequisite, pressing, primal, quintessence, ramification, requisite, rudimentary, sine-qua-non, source, systemic, ubiquitous