vast, large, grand, expansive
灝 centers on immense scale: something vast, large, grand, or expansive, often with a sense of water or fluidity.
灝 combines 氵 (water) with 顥, which likely contributes the sound and the idea of brightness or vastness. The exact historical development is uncertain.
Water 氵 combined with a grand, bright component 顥 suggests an immense body of water stretching to the horizon: vast and expansive.
For コウ, imagine a vast ocean stretching out under a bright sky, and the sound of the waves is a deep 'koh': koh -> コウ.