This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
The exact historical development of 剬 is uncertain. It visually combines 耑 and 刂, but the original semantic and phonetic roles are unclear.
The left side 耑 suggests a sprout or tip, and the right side 刂 is a knife. Imagine a knife cutting a delicate sprout, but the meaning remains uncertain.
For タン, picture a tan-colored sprout being cut by the knife: tan -> タン, though the kanji's meaning is unclear.