noun
groove worn into a shamisen player's fingernail
A physical groove that forms on the fingernail from repeated friction against the shamisen string. Specific to shamisen technique; compare 糸道 (いとみち), which can refer to the string path or the groove itself.
See also: 糸道 (いとみち)
長年三味線を弾いていると、左手の爪に糸爪ができる。
When you play the shamisen for many years, a groove called 糸爪 forms on the fingernail of your left hand.