waves, billows
灔 centers on large, rolling water movements: waves and billows. It describes the swell and surge of water, especially in a dramatic or powerful sense.
灔 combines 澧 (water) with 色, which likely contributes a phonetic element. The exact historical development is uncertain, but the water radical clearly ties it to waves and billows.
The left side 澧 suggests water, and the right side 色 looks like a colorful, swelling shape. Imagine a colorful, swelling wave rising from the water: 灔 is a billow.
For エン, picture an enormous wave ending in a curl: the end of the wave cues エン, and the wave itself is a billow.