nieceyoudaoicibaDictYouDict[niece 词源字典]
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’.
=> nephew[niece etymology, niece origin, 英语词源]
grand-youdaoicibaDictYouDict
a special use of grand (adj.) in genealogical compounds, originally with the sense of "a generation older than," first attested c. 1200, in Anglo-French graund dame "grandmother," also grandsire (late 13c.), from such use of Old French grand-, which perhaps is modeled on Latin avunculus magnus "great uncle." The partly-anglicized grandmother, grandfather are from 15c. Other such words in European languages are formed with the adjectives for "old" or "best" (Danish bedstefar) or as diminutives or pet names (Greek pappos, Welsh taid). The French formation also is the model for such words in German and Dutch. Spanish abuelo is from Latin avus "grandfather" (from PIE *awo- "adult male relative other than the father;" see uncle), via Vulgar Latin *aviolus, a diminutive or adjective substitution for the noun.

The extension of the sense to corresponding relationships of descent, "a generation younger than" (grandson, granddaughter) is from Elizabethan times. The inherited PIE root, *nepot- "grandchild" (see nephew) has shifted to "nephew; niece" in English and other languages (Spanish nieto, nieta). Old English used suna sunu ("son's son"), dohtor sunu ("son's daughter").
grand-daughter (n.)youdaoicibaDictYouDict
also granddaughter, 1610s, from grand- + daughter.
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."