The degree to which a sound's timbre conforms to a harmonic series. Harmonicity
Harmonicity can be determined arithmetically by factoring which finds the aliquot parts of a frequency.
FOR EXAMPLE:
A = 432 or 440?
432 vs 440 - Harmony is determined by having low numbers (Pythagoras). Higher numbers therefore can have many discords. A frequency is a composite or resultant of its aliquot parts.
432 = 2^4 * 3^3 are all low numbers.
440 = 2^3 * 55 * 11 are dangling higher numbers.
Therefore 432 has greater harmonicity than 440.
Of course, there is a lot more to this but the above ought to get you thinking. [see Law of Harmony]
See Also
13.23 - Degree of Concord Discord Determines
432
Degree of Harmonicity
Figure 8.14 - Some Basic Waveforms and their constituent Aliquot Parts
Harmonic
Harmony
Law of Harmony
Scale