hide
囥 centers on concealment: hiding something away from view or keeping it out of sight.
囥 combines the enclosure 囗 with 亢 inside. The exact historical origin is uncertain, but it likely expresses the idea of something being kept within a boundary, hence hiding.
The outer 囗 is like a box or enclosure, and inside is 亢. Imagine hiding something inside a box so that it cannot be seen.
For コウ, picture a hidden object inside a box that makes a hollow sound when you tap it: hollow -> コウ, and the sound reveals something is hidden inside.