1. A woman or girl with whom one has established a bond through a ritual involving the mixing or exchange of blood, often as a symbol of sisterhood and loyalty
They became blood sisters after pricking their fingers and mixing their blood together.
Elas se tornaram irmãs de sangue depois de furar os dedos e misturar seu sangue.
2. A female friend who is as close or loyal as a biological sister
My best friend is my blood sister; we've been through everything together.
Minha melhor amiga é minha irmã de sangue; passamos por tudo juntas.