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.
Required, essential, whether logically inescapable or needed in order to achieve a desired result or avoid some penalty.
Unavoidable, inevitable.