Brofrunsin 

Someone who is not related to you, but who you think of as a mixture of a brother, a friend, an uncle, or a cousin. This term is more commonly used as the shortened version: "Bro". The female version is Sisfrausin, a mixture of a sister, a friend, an aunt, and a cousin.

I'm going to go bowling with my Brofrunsin! My bro is the greatest. All the best bros are homeschooled.

Brofrunsin by Dr. Sisbro June 29, 2016