NEPHEW – son of one’s brother or sister; also an illegitimate son of an eccleasiastic, a niece, or a male or female grandchild
Merriam-Webster Online Dictionary
nephew (noun)1.
a) a son of one's brother or sister or of one's brother-in-law or sister-in-law
b) an illegitimate son of an ecclesiastic
2.
obsolete a lineal descendant , especially - grandson