Same word as nubbest:

absolute, basal, cardinal, cold, complete, congenital, connate, constitutional, deep-seated, elemental, elementary, ideal, inborn, inbred, inherent, innate, intrinsic, key, main, material, meat and potatoes, name of the game, nitty-gritty, nub, perfect, primary, prime, primitive, principal, quintessential, substratal, underlying