hill in Hunan
岣 is a rare kanji that refers to a specific hill in Hunan. Its meaning is narrowly geographical and does not extend to general hill or mountain concepts.
岣 combines 山 (mountain) with 句, which likely contributes a phonetic element. The character was created to name a specific hill, and its historical development beyond this is uncertain.
The left side 山 means mountain, and the right side 句 looks like a hook. Picture a hook-shaped hill in Hunan: 岣 is that specific hill.
For コウ, imagine a hill so steep that climbers say 'ko!' as they struggle up. The sound 'ko' cues コウ while you picture the Hunan hill.