This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
縬 combines 糸 (thread) with 戚, which may contribute sound. The exact historical development is uncertain.
The thread radical 糸 beside 戚 suggests something related to fabric or texture, but the exact meaning is unclear.
For シュク, imagine a bolt of fabric being shaken out: shook -> シュク, and the thread 糸 rustles as it unfolds.