(a.) Lying under or beneath; hence, fundamental; as, the underlying strata of a locality; underlying principles.

ab ovo basal basic basilar between the lines bottom cardinal constituent constitutive covert critical crucial cryptic delitescent dormant elemental elementary esoteric essential foundational fundamental gut hibernating hidden indispensable latent lurking material muffled mystic necessary needful obfuscated obscured occult of the essence original possible potential primal primary primitive radical rudimentary sleeping submerged substantial substantive under the surface unmanifested veiled virtual vital