Nephew and niece
A nephew is a son of one's sibling or half-sibling, and a niece is a daughter of one's sibling or half-sibling. Sons and daughters of siblings-in-law are also referred to as nephews and nieces respectively, even though there is no blood relation.
History
The word nephew is derived from the French word neveu. Historically, a nephew was the logical recipient of his uncle's inheritance if there was no son or daughter. The term 'nepotism', meaning familial loyalty, comes from the Latin term for a nephew.
Variations
Nephew – son of one's brother/sister.
Niece – daughter of one's sister/brother.
Nibling – gender-neutral term for niece or nephew.
Half-nephew – son of one's half-brother/half-sister.
Half-niece – daughter of one's half-brother/half-sister.
Nephew-in-law – son of one's sister-in-law/brother-in-law; husband of one's niece.
Niece-in-law – daughter of one's sister-in-law/brother-in-law; wife of one's nephew.
Step-nephew – son of one's stepbrother/sister, or stepson of one's brother/sister.