A step-sibling of a step-sibling.
Here's an example :
A & B had
Child 1
A &
B then got divorced, A married C and B married D.
C had Child 2 and D had Child
3 from their previous marriage.
Couple A&C and couple B&D now share childcare responsibilities of Child 1, 2 &
3 and often babysit them together.
So, while none of the three children shares blood, Child 2 &
3 have a common Step-sibling, Child 1.
Child 2 & Child
3 could be called each other's Antipodal Siblings.
"How are you and
Jimmy related?"
"Well, we're Antipodal Siblings. Him and I share the same step-sibling, Lucy. Lucy is my step-
sister cause her mom married my dad and Jimmy's step-
sister cause her dad married his mom. We're one big blended family!"