avunculate

Etymology
From.

Noun

 * 1)  The relationship between a man and his sister's children, generally her sons.
 * 2)  Among certain tribal peoples, for example, the Korowai, a special relationship between a man and a maternal uncle, and the mutual responsibilities between them.

Adjective

 * 1) Pertaining to a society where the avunculate is of central importance.
 * 2) Pertaining to a marriage to one's aunt, uncle, niece or nephew.
 * 1) Pertaining to a marriage to one's aunt, uncle, niece or nephew.