Answer:
As nouns the difference between fundamental and overtone is that fundamental is 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 while overtone is (physics|music) a tone whose frequency is an integer multiple of another; a harmonic.
As an adjective fundamental is pertaining to the foundation or basis; serving for the foundation hence: essential, as an element, principle, or law; important; original; elementary.
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