aunt-in-law

plural aunts-in-law

1. The wife 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 aunt of one's spouse.
   1. The aunt of one's husband.

      2009 August 28, contributor, Petunia Dursley, Harry Potter Wiki Petunia would later become an aunt-in-law to Harry's wife Ginevra Weasley and a great-aunt to Harry and Ginny's three children; James Sirius, Albus Severus,

   2. The aunt of one's wife.