child's sash; attached cord
A cord or sash attached to a child's garment, traditionally used to keep the garment closed or to prevent the child from wandering too far. The term is somewhat dated and may be encountered in historical or traditional contexts.
In old children's clothing, attached sashes were often used.
Compound of 付け (tsuke, 'attaching') + 紐 (himo, 'cord, string'). The exact historical derivation is uncertain, but the term literally means 'attached cord'.