pibling
Used especially as a gender-neutral term: the sibling or sibling-in-law of one's parent; one’s uncle or aunt.
rare
We measured a [representing assortative mating] repeatedly, comparing the correlations of piblings (parents' siblings; avuncular relatives) with those of piblings-in-law[…]; first cousins with first-cousins-in-law[…]; and first-cousins-once-removed with first-cousins-once-removed-in-law[…].
Where it comes from
Blend of parent (noun) + sibling (noun).
Adapted from the Wiktionary entry pibling (CC BY-SA 4.0).