entrenchment, bank, low wall
隖 centers on a defensive earthwork: a low wall or bank used for entrenchment and protection.
隖 combines ⻖ (mound, hill) with 烏, which likely contributes the sound. The character is associated with earthworks and defensive structures.
The mound radical ⻖ on the left suggests an earthen structure, while 烏 (crow) on the right can be imagined as a bird perched on a low wall or bank. Picture a crow sitting on a defensive earthwork.
For オ, imagine an old low wall where crows gather: 'old' sounds like オ, and the crows (烏) perch on the entrenchment.