Source : Webster's Revised Unabridged Dictionary (1913)

Nephew \Neph"ew\ (n[e^]f"[-u]; in England n[e^]v"[-u]; 277), n.
   [OE. neveu, nevou, nevu, fr. F. neveu, OF. also, nevou, L.
   nepos; akin to AS. nefa, D. neef, G. neffe, OHG. nevo, Icel.
   nefi a kinsman, gr. ne`podes, pl., brood, young, Skr.
   nep[=a]t grandson, descendant. [root]262. Cf. {Niece},
   {Nepotism}.]
   1. A grandson or grandchild, or remoter lineal descendant.
      [Obs.]

            But if any widow have children or nephews [Rev. Ver.
            {grandchildren}].                     --1 Tim. v. 4.

            If naturalists say true that nephews are often liker
            to their grandfathers than to their fathers. --Jer.
                                                  Taylor.

   2. A cousin. [Obs.] --Shak.

   3. The son of a brother or a sister, or of a brother-in-law
      or sister-in-law. --Chaucer.

Source : WordNet®

nephew
     n : a son of your brother or sister [ant: {niece}]