Niece and nephew in the context of "Sibling-in-law"

An aunt is a female individual who is a sibling of a parent or married to a sibling of a parent. Aunts who are related by birth are second-degree relatives. Alternate terms include auntie or aunty.

Aunt, auntie, and aunty also may be titles bestowed by parents and children to close friends of one or both parents who assume a sustained caring or nurturing role for the children. Children in some cultures and families may refer to the cousins of their parents as aunt or uncle due to the age and generation gap. The word comes from Latin: amita via Old French ante and is a family relationship within an extended or immediate family.

An uncle is usually defined as a male relative who is a sibling of a parent or married to a sibling of a parent, as well as the parent of the cousins. Uncles who are related by birth are second-degree relatives. The female counterpart of an uncle is an aunt, and the reciprocal relationship is that of a nephew or niece. The word comes from Latin: avunculus, the diminutive of avus (grandfather), and is a family relationship within an extended or immediate family. A popular colloquial term in English is Unc.

In some cultures and families, children may refer to the cousins of their parents as uncle (or aunt). It is also used as a title of respect for older relatives, neighbours, acquaintances, family friends, and even total strangers in some cultures, for example Aboriginal Australian elders. Using the term in this way is a form of fictive kinship.