uncle-in-law

plural uncles-in-law

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, William Lindsay, Inquiry into the Christian law, as to the relationships which bar marriage, page 86

2. The uncle of one's spouse.
   1. The uncle of one's husband.

      2012 August 11, anonymous, Vernon Dursley, Harry Potter Wiki 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.

   2. The uncle of one's wife.