This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
The exact historical development of 脠 is uncertain. It combines the flesh component ⺼ with 延, but the original meaning and formation are unclear.
With ⺼ (flesh) on the left and 延 (prolong) on the right, imagine stretching or preserving meat, but the actual meaning is uncertain.
For セン, picture a thousand (千, せん) strips of meat being stretched out: 千 -> セン, and the flesh component ⺼ is being prolonged.