Pibling, which I think is the same but it can also apply as gender neutral niece/nephew
I've always heard "pibling" for gender-neutral aunt/uncle and "nibling" for gender-neutral niece/nephew, but I feel like "nibling" has much better mouthfeel and is way cuter by comparison. I always joke with my niblings that they can call me their Ankle, but imo there's just not a GREAT all-purpose word for it yet
