Necessary, essential for life or some process.
Elementary, simple, fundamental, merely functional.
Of or pertaining to a base; having a pH greater than 7.
Unremarkable or uninteresting; boring; uncool.
An elementary building block, e.g. a fundamental piece of knowledge.
A necessary commodity, a staple requirement.
Basic training.
Absolutely necessary or requisite; that one cannot do without.
Unbendable, that cannot be set aside or ignored.
A thing that is not dispensable; a necessity.