nieceyoudaoicibaDictYouDict
niece: [13] Niece comes ultimately from *neptī-, the feminine form of Indo-European *nepōt- (source of English nephew). This passed into Latin as neptis ‘granddaughter, niece’, which in post-classical times became *neptia. Old French took it over as niece – whence English niece. *Neptī- also had a Germanic descendant, *niptiz, which now survives only in German nichte and Dutch nicht ‘niece’.
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niece (n.)youdaoicibaDictYouDict
c. 1300, from Old French niece "niece, granddaughter" (12c., Modern French nièce), earlier niepce, from Latin neptia (also source of Portuguese neta, Spanish nieta), a more decidedly feminine form of neptis "granddaughter," in Late Latin "niece," fem. of nepos "grandson, nephew" (see nephew). Replaced Old English nift, from Proto-Germanic *neftiz, from the same PIE root (Old English also used broðordohter and nefene).

Until c. 1600, it also commonly meant "a granddaughter" or any remote female descendant. Cognate with Spanish nieta, Old Lithuanian nepte, Sanskrit naptih "granddaughter;" Czech net, Old Irish necht, Welsh nith, German Nichte "niece."