gay, deep
潚 centers on deep, clear water. The meaning "gay" is likely an archaic or rare sense, possibly related to a cheerful, clear state, but the primary idea is depth and clarity of water.
潚 combines 氵 (water) with 肅, which likely contributes the sound and may relate to depth or solemnity. The exact historical development is uncertain.
Water 氵 beside 肅, which looks deep and solemn. Imagine a deep, clear pool of water that is so still it feels almost solemn.
For シュク, imagine a deep pool of water that is so clear you can see a shoe at the bottom: shoe -> シュ, and the deep water is cool: cool -> ク, together shoe-cool -> シュク.