三さんの糸いと

noun

third string (of a shamisen, etc.)

Refers specifically to the third string of a shamisen or similar traditional Japanese stringed instrument. The term is technical and used in musical contexts.

• 三さんの糸いとが切きれたので、新あたらしいものに張はり替かえた。

  The third string broke, so I replaced it with a new one.