This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
縜 combines 糸 (thread) with 員, which likely contributes sound. The exact historical development is uncertain.
With 糸 (thread) on the left and 員 on the right, picture a thin cord or string. The kun reading ほそひも suggests a slender thread.
For イン, imagine a thin thread being wound into an inn: inn -> イン, and the thread is stored there.