[joelfried]

I'm a bit surprised you've never heard of the spouse of a parental sibling called an uncle as well. To make that more explicit: my father's sister is my aunt, and her husband is my uncle.

[flufferstutter]

That is definitely common in my experience. Now calling the brother of my parent’s brother’s wife “uncle” might be a bit of stretch.

[kaashif]

Oh, I meant brother in law too, actually. But my point is, anything beyond that isn't something I've heard.