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)
When you play the shamisen for many years, a groove called 糸爪 forms on the fingernail of your left hand.
Compound of 糸 (いと, 'string') and 爪 (つめ, 'nail'), with rendaku voicing of つめ to づめ. The term directly describes the groove worn into the nail by the string.