co-aunt
noun 2
Definitions
noun
1
of a woman, an aunt of one's niece or nephew who is not one's sister; a co-sister-in-law as common aunt to the children of two women's married siblings.
2
a woman's sister, as aunt in common to the children of a third sibling
A few years ago, my sister and co-aunt Judy started flying [our niece and nephew] Violet and Dash down to California to spend a week with her
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