This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
The exact historical development of 氙 is uncertain. It visually combines 气 (gas, vapor) with 山 (mountain), but the original purpose and meaning are unclear.
The outer shape 气 suggests something related to gas or vapor, and the inner 山 is a mountain. Imagine a mysterious mountain mist, but remember the actual meaning is uncertain.
For セン, picture a thousand (千, せん) mountain peaks shrouded in vapor: 千 -> セン, and the misty mountains match the shape of 氙.
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