harmony vs congruence

harmony and congruence both are nouns.

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

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

Other hyponyms of harmony include congruity, congruousness, composedness.

harmony (noun)	congruence (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