This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
The exact historical development of 夵 is uncertain. It visually combines 大 (big) on top and 小 (small) on the bottom, but this may be a later simplification or variant form.
With 大 (big) on top and 小 (small) on the bottom, 夵 looks like something big shrinking to small, but since its meaning is unclear, treat it as a shape to recognize rather than a concept to memorize.
For エン, imagine a big 大 and small 小 shape merging into a single yen coin: yen -> エン, and the coin's value is uncertain like the kanji's meaning.