unpatterned silk, loose
縵 centers on plain, unadorned silk without a pattern, and by extension something loose or unstructured.
縵 combines 糸 (silk) with 曼, which likely contributes the sound and the idea of something extended or loose, giving the sense of plain, unpatterned silk.
The silk thread 糸 on the left is combined with 曼, which suggests something stretched out and plain. Imagine a bolt of loose, unpatterned silk flowing smoothly.
For マン, picture a man wrapping himself in a long, plain silk robe: man -> マン, and the silk is loose and unpatterned.
—
smooth unlettered back surface of an old "zeni" coin