Sentence:  "Of course she's your aunt Callie. She's married to your uncle Rod." Kelsey threw her head back and laughed. “Then she's a <WSD>double aunt</WSD>.” Dana coughed. "Do you want some pie?" "What's a <WSD>double aunt</WSD>?" Callie tilted her head, a half smile curving her lips. "You're married to my Uncle Rod, Dad's brother, and you're also Mom's sister." 
Meaning of the word marked with <WSD> tags:  A woman who is one's aunt in two ways, e.g. being a sister of one parent and the wife of a sibling of the other.