I was idly wondering a few days ago whether there’s a non-gendered term for an aunt or uncle. Such a term might be useful (for example) for referring collectively to a group of aunts and uncles, or for referring to a specific aunt-or-uncle of unknown gender, or for referring to a nonbinary-gendered aunt or uncle.
But before I got around to posting the question, Mya coincidentally asked the same question.
It turns out that there isn’t a widely used term in English. But see comments on Mya’s post for various suggestions, serious and otherwise.
A couple of the proposed terms, notably parsib and pibling, are in use by various people, but as Mya notes, terms based on the word sibling “aren’t inclusive of the way ‘aunt’ & ‘uncle’ are often honorary titles for family friends or community adults.”
I’ve also seen auncle, but as with most neologisms I come across, I find that aesthetically unsatisfying.
Ann Leckie’s novel Provenance uses the term nuncle to refer to third-gendered parent-siblings, but (a) that’s specifically referring to a particular third gender, not a gender-neutral term, and (b) it’s a traditional word for uncle in some English dialects.
I think my personal favorite of the various terms suggested in the discussion on Mya’s post is ommer. I don’t know the derivation, but I like the sound of it. Even though I like being Uncle Jed to various kids, I think I would be okay with someone calling me Ommer Jed.
PS: Maybe after we find a gender-neutral noun, the adjective form (corresponding to avuncular) will become obvious, but in the meantime, that too is lacking in English. I personally am fond of avauntular, but only as a joke. I suppose the adjective form of ommer would be something like ommerical? Or ommerish?