1. noun
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.
2. adjective
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.
See Also: fundament
Wikipedia foundation.