obscured eyesight, to feel ashamed
瞢 centers on a state of obscured or failing eyesight, and by extension the shame or confusion that can come from not seeing clearly.
瞢 combines 目 (eye) with a phonetic element that includes ⺾ and 冖. The exact historical development is uncertain, but the character is associated with dim or blurred vision.
The top ⺾ (grass) over 冖 (cover) suggests something covering the eye 目 below, like a veil of grass obscuring clear sight. This blurred vision leads to feelings of shame.
For ボウ, imagine a bow (as in bow and arrow) being drawn, but your obscured eyesight makes you miss the target, causing shame: bow -> ボウ.