first harmonic vs fundamental frequency

first harmonic and fundamental frequency both are nouns.

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

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

first harmonic and fundamental frequency: the lowest tone of a harmonic series

Other synonyms of first harmonic include fundamental.

first harmonic (noun)	fundamental frequency (noun)
the lowest tone of a harmonic series	the lowest tone of a harmonic series