armonizar

To harmonize — musically (armonizar una melodía, to add harmony to a melody) or, just as commonly, figuratively: to make things compatible or consistent (armonizar leyes, intereses, colores). Broadly used across music, law, and design.

• El compositor armonizó la melodía para cuatro voces. — The composer harmonized the melody for four voices.
• Hay que armonizar los intereses de ambas partes. — The interests of both parties need to be reconciled/harmonized.
• Los colores del salón armonizan bien con los muebles. — The colors of the living room harmonize well with the furniture.

Using armonizar as a simple synonym of combinar — armonizar specifically implies making things work together pleasingly or consistently, resolving tension between them, not just putting things side by side.