(1):

(a.) Having relations or properties bearing some resemblance to those of musical consonances; - said of certain numbers, ratios, proportions, points, lines. motions, and the like.

(2):

(a.) Concordant; musical; consonant; as, harmonic sounds.

(3):

(a.) Relating to harmony, - as melodic relates to melody; harmonious; esp., relating to the accessory sounds or overtones which accompany the predominant and apparent single tone of any string or sonorous body.