This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
膞 combines the flesh radical ⺼ with 專, which likely contributes a phonetic element. The exact historical development is uncertain.
The left side ⺼ suggests flesh or body, and the right side 專 is a complex shape. Without a clear meaning, picture a rare body part or a cut of meat (きりみ) that is hard to name.
For セン, imagine a rare cut of meat being sent (セン) to a specialist for identification: sent -> セン.