This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
The exact historical development of 阽 is uncertain. It combines the mound radical ⻖ with 占, but the original semantic and phonetic roles are unclear.
With no clear meaning, picture the mound ⻖ beside 占 as a precarious cliff edge about to crumble, matching the kun-reading sense of 'about to collapse'.
For エン, imagine the cliff edge (⻖) ending in a sudden drop: end -> エン, as the ground gives way.