grass, grassy field
莽 centers on thick, wild grass or a grassy field. The idea is of dense, untamed vegetation.
莽 combines the grass radical ⺾ with a lower part that historically depicted a dog among thick vegetation, conveying the idea of dense grass or a grassy field.
The top ⺾ is grass, and the inside 犬 is a dog. Imagine a dog lost in a vast, overgrown grassy field, barely visible above the thick grass.
For ボウ, picture a bow (as in bow and arrow) lying hidden in the tall grass: bow -> ボウ, and you can barely see it in the grassy field.