It must have been written .
Usually it means a brother-in-law. But, in this movie it means blood brothers: 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.
![enter image description here](