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.
The third string broke, so I replaced it with a new one.
Compound of 三 (san, 'three') + の (no, possessive particle) + 糸 (ito, 'string'). The term follows the naming pattern for shamisen strings: 一の糸 (first string), 二の糸 (second string), 三の糸 (third string).