Coustwin 

A first cousin that is the same age as you and is in the same grade as you

Princess 1: Are you two twins?
Princess 2: Yes! We're coustwins!
Princess 1: What's a coustwin?
Prince 1: It's a first cousin that's the same age as you and is in the same grade as you.

Coustwin by Princess Zoë December 4, 2016

cousting 

cock jousting. Like the medieval version, but using your cock as the lance. Not to be confused with clousting

To amuse themselves Eddy and James would often indulge in a spot of cousting

cousting by Philippe Flopp May 4, 2006