This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
The exact historical development of 囦 is uncertain. It visually combines 囗 (enclosure) with 水 (water), but its original meaning and origin are unclear.
Water 水 trapped inside an enclosure 囗 suggests a deep pool or abyss, but the actual meaning is uncertain.
For エン, imagine a round enclosure 囗 holding water 水, like a yen coin dropped into a wishing well: yen -> エン.