This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
The exact historical development of 阥 is uncertain. It combines ⻖ (mound/hill) with 水 (water), but the original meaning and component relationship are unclear.
The left side is a mound or hill, and the right side is water. Picture a hill beside water, but the overall meaning is unclear.
For イン, imagine an inn built on the hill by the water: inn -> イン, and the inn sits between the mound and the stream.