I. adjective
1.
forming or affecting the groundwork, roots, or lowest part of something
the fundamental rules of poetry
Synonyms: basal, basic, bottom, foundational, meat-and-potatoes, primary, radical, underlying
Related Word: primal, prime, primordial; elemental, elementary
Contrasted words: incidental
2.
Synonyms: elemental 1, basic, elementary, essential, primitive, substratal, underlying
3.
Synonyms: essential 2, cardinal, constitutive, vital
Related Word: indispensable, necessary, needful, requisite; dominant, paramount
II. noun
1.
Synonyms: principle 1, axiom, law, principium, theorem
Related Word: component, constituent, element, factor
2.
Synonyms: essential 1, basic, element, part and parcel, rudiment
3.
usually fundamentals plural
Synonyms: alphabet 2, ABC's, elements, grammar, principles, rudiments