unclear, be astonished
惘 centers on a mental state of confusion or being lost: something is unclear, or a person is so astonished they cannot think straight.
惘 combines the heart radical 忄 with 罔, which likely contributes both sound and the idea of being entangled or lost, giving a mental state of confusion or astonishment.
The heart 忄 beside 罔, which looks like a net or tangled web, suggests a mind caught in confusion: unclear thoughts or being so astonished you feel mentally tangled.
For ボウ, imagine a confused person staring at a tangled net and saying 'bow' (as in taking a bow) in astonishment: bow -> ボウ, and the heart is tangled in the web.