(n) A double uncle is man who is someone's mother's brother and also that person's father's brother. In other words, a double uncle is an uncle on both sides of the family. For a double uncle to exist, a child must be a product of incest between two siblings, and the parents must share a brother.
Tyrion Lannister from A Song of Ice and Fire / Game of Thrones is probably the most well known double uncle. His double nephews don't appreciate him like a double uncle should be appreciated.

Person A: Dude, Tyrion is freaking awesome. He's probably my favourite character at the moment.

Person B: Yeah, it's a shame he's that Joffrey faggot's double uncle.

-----

Person A: My double uncle said he'd get us all ice creams!

Person B: Double uncles are the greatest!

Double Uncle: Now get back in my van, kids. And don't scream.
by Faguette February 22, 2014
Get the Double uncle mug.
Son of their grandparent’s full sibling with the other grandparent’s full sibling.
My double-first cousin-uncle is a good person.
by Hgcloziw November 23, 2019
Get the double-first cousin-uncle mug.
Son of their grandparent’s full sibling with the other grandparent’s full sibling.
My double-cousin-uncle is a good person.
by Hgcloziw November 23, 2019
Get the double-cousin-uncle mug.
Son of a paternal grandmother with maternal grandfather, in other words, maternal half-brother of one's father and paternal half-brother of one's mother at the same time or also is the son of a maternal grandmother with paternal grandfather, in other words, paternal half-brother of one's father and maternal half-brother of one's mother at the same time.
My double-half-uncle is a good person.
by Hgcloziw November 23, 2019
Get the double-half-uncle mug.
1- Half-brother of mother and of father at the same time.
2- Son of maternal grandmother (mother's mother) and of paternal grandfather (father's father) at the same time.
3- Son of paternal grandmother (father's mother) and of maternal grandfather (mother's father) at the same time.
4- Two parents's half-brother.
My double-half-uncle is a good person.
by Peter12369 October 21, 2021
Get the double-half-uncle mug.
1- Half-brother of mother and of father at the same time.
2- Son of maternal grandmother (mother's mother) and of paternal grandfather (father's father) at the same time.
3- Son of paternal grandmother (father's mother) and of maternal grandfather (mother's father) at the same time.
My double-half-uncle is a good person.
by Peter12369 October 21, 2021
Get the double-half-uncle mug.
Son of their great-grandparent’s full sibling with the other great-grandparent’s full sibling.
My double-great-cousin-uncle is a good person.
by Hgcloziw November 23, 2019
Get the double-great-cousin-uncle mug.