Language: Mandarin Chinese
Source: Classical literature

Description

Yāodāo xìzi (腰刀繫子) means "saber lanyard". It's the wrist strap that helps secure the saber to the wrist.¹

They are usually made of silk, tied together with string or in a ball knot.

Original xìzi on a fine Qing imperial saber. Sold by Mandarin Mansion in 2018.

A simple xìzi on a Qing bannerman saber.

Officer Sainku. Imperial Guard of the 3rd class. Baturu. Notice the lanyard wrapped firmly around his hand.
Ethnological Museum of Hamburg.

References
1. Wuti Qingwen Jian (五體清文鑑)or "Five languages compendium", a Qing imperial dictionary in Manchu, Mongolian, Uighur, Tibetan and Chinese of 1766. Published under the Qianlong emperor.