The definition of a grandniece is the female child of your niece or nephew.
An example of a grandniece is your brother’s granddaughter.
A daughter of one's nephew or niece.
- In November 1856 he married Adele Cutts, a Maryland belle, a grandniece of Dolly Madison, and a Roman Catholic, who became the leader of Washington society, especially in the winter of 1857-1858, when Douglas was in revolt against Buchanan.
- The family gathered in this three-storeyed building, with its back windows looking over the Elbe and its front door opening on a great garden, was latterly Luther and his wife, their three sons and two daughters, Magdelena von Bora, Catherine's aunt, two orphan nieces and a grandniece.