concord
Meaning: harmonious agreement
Usage: Julie and Harold began the evening with a disagreement, but ended it in a state of perfect concord.
consonant
Meaning: in harmony
Usage: The singers’ consonant voices were beautiful.
congruity
Meaning: the quality of being in agreement
Usage: Bill and Veronica achieved a perfect congruity of opinion.
rapport
Meaning: mutual understanding and harmony
Usage: When Margaret met her paramour, they felt an instant rapport.