harmony vs congruity

harmony and congruity both are nouns.

Word	Noun	Adjective	Verb	Adverb
harmony	Yes	No	No	No
congruity	Yes	No	No	No

As nouns, congruity is a hyponym of harmony; that is, congruity is a word with a more specific, narrower meaning than harmony:

Other hyponyms of harmony include congruence, congruousness, composedness.

harmony (noun)	congruity (noun)
an agreeable sound property	the quality of agreeing; being suitable and appropriate
compatibility in opinion and action
agreement of opinions
the structure of music with respect to the composition and progression of chords
a harmonious state of things in general and of their properties (as of colors and sounds); congruity of parts with one another and with the whole