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1.
The son of your or your biological sibling's godparents, brother of your godsister, etc.

A boy you grew up with, a good friend that is like a brother to you
Friend 1: That's my brother.
Friend 2: I thought you were an only child.
Friend 1: Yeah, only biologically. That's my godbrother.
by lordkeittarro June 27, 2011