adjective

1. harmonious in feeling or effect; agreeing
2. Math. designating or of a harmonic progression
3. Music
   1. of or pertaining to harmony rather than to melody or rhythm
   2. of or pertaining to a harmonic

Etymology: L harmonicus < Gr harmonikos < harmonia, harmony

noun

1. an alternating-current voltage or current or a component of such voltage or current, whose frequency is some integral multiple of a fundamental frequency
2. any of the pure tones making up a composite tone, including the fundamental and its upper partials or overtones; partial tone