What word could I use to define someone who is not kin to me but I regard to be better than a friend?
There are only idioms for such a thing.
- Thick as thieves
- Brother from another mother
- Like brothers (as in, we're like brothers)
- Soul brother
I have plenty of friends whom I've known since we were born and I have yet to come across a single word that can sum up the idea of being "like brothers"... Most of the time, I just say "We might as well be brothers"
My "best friend", "BFF", "closest [dearest] friend", or my "blood brother"
The initialism (or abbreviation) for Best Friend Forever
a way of referring to a person's best friend
Blood brother can refer to one of two things: a male related by future birth, or two or more men not related by birth who have sworn loyalty to each other. This is in modern times usually done in a ceremony, known as a blood oath, where having each person make a small cut, usually on a finger, hand or the forearm, and then the two cuts are pressed together and bound, the idea being that each person's blood now flows in the other participant's veins. In modern times, some gangs have also been rumored to make blood pacts.
See Cambridge Dictionary for a very similar, but less detailed definition than Wikipedia's.
(There are some users who turn up their noses at Wikipedia)
brother from another mother noun a good friend that is more like a brother. Also sister from another mister. He's my brother from another mother.
Which is weird since actual half brothers could literally be brothers from different mothers.