Nouns

(n)harmonica tone that is a component of a complex sound
(n)harmonicany of a series of musical tones whose frequencies are integral multiples of the frequency of a fundamental

Adjectives

(a)harmonicof or relating to harmony as distinct from melody and rhythm“subtleties of harmonic change and tonality” (Ralph Hill)
(a)harmonicof or relating to harmonics
(a)harmonicof or relating to the branch of acoustics that studies the composition of musical sounds“the sound of the resonating cavity cannot be the only determinant of the harmonic response”
(s)harmonic, sympatheticrelating to vibrations that occur as a result of vibrations in a nearby body“sympathetic vibration”
(s)consonant, harmonic, harmonical, harmonized, harmonisedinvolving or characterized by harmony