curtain
幨 centers on a hanging cloth used to cover or separate: a curtain.
幨 combines 巾 (cloth) with 詹, which likely contributes the sound. The exact historical development of 詹 is uncertain, but the character as a whole is associated with cloth coverings.
The left side 巾 is a cloth, and the right side 詹 looks like a complex hanging structure. Picture a large cloth hanging from a rod, forming a curtain.
For セン, imagine a scene where a curtain is drawn to reveal a thousand (千, せん) stars: 千 -> セン, and the curtain opens to the night sky.