Underlying
Part of speech: adjective
Definition: lying underneath basic or fundamental implicit
Example sentence: There is a lurking sense that there is a kind of seedy corruption underlying a lot of public life today. But while journalism does a very good job of describing that corruption, it is failing to bring it into a bigger focus. To explain what it is all about.
Fundamental
Part of speech: adjective
Definition: Pertaining to the foundation or basis; serving for the foundation. Hence: Essential, as an element, principle, or law; important; original; elementary; as, a fundamental truth; a fundamental axiom.
Part of speech: noun
Definition: A leading or primary principle, rule, law, or article, which serves as the groundwork of a system; essential part, as, the fundamentals of linear algebra.
Example sentence: Work is about more than making a living, as vital as that is. It's fundamental to human dignity, to our sense of self-worth as useful, independent, free people.