1.NounThe relationship between a man and his sister's children, generally her sons.
2.NounAmong certain tribal peoples, for example, the Korowai, a special relationship between a man and a maternal uncle, and the mutual responsibilities between them.
3.AdjectivePertaining to a society where the avunculate is of central importance.
"avunculate society"
4.AdjectivePertaining to a marriage to one's aunt, uncle, niece or nephew.