Nieta, 12th cent; nieto, 11th cent. The feminine nieta is the original form, tracing back to Vulgar Latin nepta "granddaughter," from Latin neptis 'id.'
From Proto-Italic *nepti- 'id.' From Proto-Indo-European *h2nep-t-ih1/2 'id.'
Old Lithuanian neptė "granddaughter"
Sanskrit neptī́- "granddaughter," Young Avestan napti- 'id.'