to look upward
厃 centers on the action of looking upward, as its sole given meaning suggests. It is a rare character with no broader conceptual cluster.
The historical origin of 厃 is uncertain. It visually combines ⺈ (a person bent over) and 厂 (a cliff), which may suggest a person looking up from under a cliff, but this is speculative.
A person ⺈ stands at the base of a cliff 厂 and looks upward to see the top.
For セン, imagine a person looking up at a cliff and seeing a cent (coin) perched on the edge: cent -> セン.