Synonyms for Harmonic (same or very similar meaning)
WordNet sense 1 (involving or characterized by harmony):
consonant, harmonical, harmonised, harmonized, in harmonyWordNet sense 2 (musically pleasing):
harmoniousWordNet sense 3 (relating to vibrations that occur as a result of vibrations in a nearby body):
sympatheticFrom the ODE community, based on WordNetadd/edit