large, mix
厖 centers on something large in scale or mixed in nature, often implying a big, blended mass. The two given meanings connect through the idea of a large, mixed collection.
厖 combines 厂 (cliff) with 尨, which likely contributes both sound and the idea of something shaggy or mixed. The exact historical development is uncertain.
Under a cliff (厂), a shaggy, mixed-up creature (尨) looks large and blended together. Picture a big, furry beast made of many mixed parts.
For ボウ, imagine a large mixed-up bow (as in a ribbon) under the cliff: bow -> ボウ, and the bow is huge and tangled.