constant, regular, persistent
恆 centers on steadiness over time: something that is constant, regular, or persistent without interruption.
恆 combines 忄 (heart/mind) with 亙, which likely contributes both sound and the idea of spanning or extending, suggesting a constant state of mind.
The heart radical 忄 beside 亙, which looks like something stretching across, suggests a heart that stays steady and persistent over time.
For コウ, imagine a constant, regular beat like a こう (kō) drum keeping time: こう -> コウ, and the heart stays steady with the rhythm.