obstruct, distress, narrow
阨 centers on being blocked or squeezed into a tight, difficult space: a narrow passage that obstructs movement and causes distress.
阨 combines ⻖ (mound, hill) with 厄, which likely contributes both sound and the idea of a narrow or difficult pass. The exact historical development is uncertain.
The mound radical ⻖ suggests a steep hill, and 厄 looks like a person squeezed under a roof. Picture a narrow mountain pass where the path is blocked and you feel distressed.
For ヤク, imagine a yak stuck in a narrow mountain pass, blocking the way: yak -> ヤク, and the yak's distress matches the kanji's meaning.