nephewyoudaoicibaDictYouDict[nephew 词源字典]
nephew: [13] Nephew goes back ultimately to Indo-European *nepōt-, which denoted a range of indirect male descendants, including ‘grandson’ and ‘nephew’. Among its offspring were Greek anepsiós ‘nephew’, Sanskrit nápāt ‘grandson’, Germanic *nebon (source of German neffe and Dutch neef ‘nephew’), and Latin nepōs ‘nephew, grandson’ (source of English nepotism [17], etymologically ‘favouring one’s nephews’).

This passed into Old French as neveu, from which English got nephew (replacing the related native English term neve). The corresponding Indo-European feminine form was *neptī-, which is the ultimate source of English niece.
=> nepotism, niece[nephew etymology, nephew origin, 英语词源]
nephew (n.)youdaoicibaDictYouDict
c. 1300, from Old French neveu (Old North French nevu) "grandson, descendant," from Latin nepotem (nominative nepos) "sister's son, grandson, descendant," in post-Augustan Latin, "nephew," from PIE *nepot- "grandchild," and in a general sense, "male descendant other than son" (cognates: Sanskrit napat "grandson, descendant;" Old Persian napat- "grandson;" Old Lithuanian nepuotis "grandson;" Dutch neef; German Neffe "nephew;" Old Irish nia, genitive niath "son of a sister," Welsh nei). Used in English in all the classical senses until meaning narrowed in 17c., and also as a euphemism for "the illegitimate son of an ecclesiastic" (1580s). The Old English cognate, nefa "nephew, stepson, grandson, second cousin" survived to 16c.