hill
阤 centers on a hill or slope, often with a sense of collapsing or crumbling terrain.
阤 combines the hill radical ⻖ with 也, which likely contributes a phonetic element. The exact historical development is uncertain.
The left side ⻖ is a hill, and the right side 也 looks like a crumbling slope. Picture a hillside that is starting to collapse.
For チ, imagine a hill made of cheese that starts to crumble: cheese -> チ, and the hill collapses.