noun
groove in a shamisen player's fingernail
A physical groove worn into the fingernail from repeated friction against the shamisen string. Specific to shamisen performance.
長年三味線を弾いていると、爪に糸道ができる。
Playing the shamisen for many years creates a groove in the fingernail.
noun
shamisen playing ability
Metaphorical extension: the groove in the nail comes to represent the player's skill or experience. Used in contexts discussing a performer's proficiency.
彼の糸道はまだ浅いが、熱心に稽古している。
His shamisen skill is still shallow, but he practices diligently.