uncle-in-law

noun4

1. •
   The husband of one's uncle or aunt (parent's sibling).

   • Between uncle and aunt-in-law, or uncle's wife, you have a connection of affinity, and you have the same between aunt and uncle-in-law, or aunt's wife. [sic] — 1871
2. •
   The uncle of one's spouse.
3. •
   The uncle of one's husband.

   • Vernon would later become an uncle-in-law to Harry's wife, Ginny and a great-uncle to Harry and Ginny's children, James Sirius Potter, Albus Severus Potter and Lily Luna Potter. — 2012
4. •
   The uncle of one's wife.