cuticle of bamboo plant
篛 refers specifically to the cuticle or outer skin of a bamboo plant. It is a narrow botanical term without broader abstract extensions.
篛 combines 竹 (bamboo) with 弱, which likely contributes a phonetic element. The exact historical development is uncertain, but the structure suggests a phono-semantic compound related to bamboo.
The top 竹 is bamboo, and the bottom 弱 suggests something weak or thin. Picture the thin, delicate cuticle peeling off a bamboo stalk.
For ジャク, imagine a jacket made of thin bamboo cuticle: jacket -> ジャク, and the jacket is as delicate as the bamboo skin.