fundamental vs first harmonic

fundamental and first harmonic both are nouns.

Word	Noun	Adjective	Verb	Adverb
fundamental	Yes	Yes	No	No
first harmonic	Yes	No	No	No

As nouns, fundamental and first harmonic are synonyms defined as:

Other synonyms of fundamental include fundamental frequency.

fundamental (noun)	first harmonic (noun)
the lowest tone of a harmonic series	the lowest tone of a harmonic series
any factor that could be considered important to the understanding of a particular business

fundamental (adjective)	first harmonic (adjective)
being or involving basic facts or principles
serving as an essential component
far-reaching and thoroughgoing in effect especially on the nature of something