1. the quality or state of being in agreement, accord, or pleasing combination
2. the quality of being musically pleasing or consonant in sound

Examples

• The harmoniousness of the team's efforts led to their success.
• The harmoniousness between the violin and cello created a beautiful duet.
• She appreciated the harmoniousness of the color scheme in the room.
• The harmoniousness of their relationship was evident to everyone around them.
• The composer sought to achieve harmoniousness in every movement of the symphony.
• The harmoniousness of nature's design never ceases to amaze scientists.