This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
嵪 combines 山 (mountain) with 高 (tall/high), likely suggesting a high or steep mountain. The exact historical development is uncertain.
A mountain 山 that is high 高: imagine a towering, steep peak. The kanji likely relates to a high mountain or hard, barren soil, but its meaning is obscure.
For コウ, picture a high mountain peak where a lone crow (コウ) perches: crow -> コウ, and the mountain is so high only a crow can reach it.