Co-brother is a very South-India specific word. However, the usage is so well prevalent out here that even Collins Dictionary notes this usage as
"since, wife's brother is brother-in-law, to avoid all confusion regarding relation, sister-in-law's husband can be called co-brother. In fact, this term is being used in India, mostly among English speaking South Indians."
Originally Posted by Crazy_Bean
Even if we are talking about cars, Its a 6 for my car
Bingo! I was going to say that. In both my cars its 6 there.