noun
harmony
HAR-muh-nee/ˈhɑːrməni/
A pleasing fit among parts acting together.
The family works in harmony while tending the flowering garden bed.

Etymology
Greek harmonia could mean a physical joining, as of ship-planks, as well as musical concord. That image of fitting things together connects pleasing sounds with agreement among people or parts.
In context
do you know what harmony is it's when people sing together and it it sounds nice
More examples
- The neighbors live in harmony despite their different backgrounds.
- Their voices blend in harmony during the final chorus.
- The song's rich harmonies give it a warm, full sound.
Forms
harmony · harmonies
harmonious adjective — Having parts that fit together pleasingly.
harmonize verb — To bring into agreement or pleasing balance.