Sentence:  I've just paid one to my <WSD>double aunt</WSD>.' Phelan ventured to ask what relationship that might be. ' She's my father's aunt first, and then she's mine next, and so she is really two aunts,' he explained. ' 
Meaning of the word marked with <WSD> tags:  A woman who is the aunt of exactly two people, especially when those two people are twins.