Gēng

A large rope, or a rope or string drawn tight.

The left part 糸 is the thread component; 恒 on the right serves as a sound clue. The Shuowen Jiezi, a dictionary from the Eastern Han, records the related form 緪 for “large rope” and also gives a sense of “tight.”

The history links a substantial cord with the state of being taut: the word can name the rope itself or describe a stretched string.

Why does 縆 appear beside strings and bridges?

Because it names a cord and its taut state.

In 縆瑟, 瑟 is a traditional Chinese plucked zither, and its strings are drawn tight. Classical texts also use 縆 for ropes used to span crossings or bridge water.

The setting supplies the nuance: a physical rope in one passage, tension in a string in another.

Is 縆 the same as 緪 or 絚?

緪, 絚, and 絙 are recorded variants; 繩 is a separate rope word.

The 縆 vs 繩 distinction is one of scope: 縆 is specialized for a large rope or taut string, while 繩 is the general word for rope.