Hamshirah means sister.
This word has its origins in persian but is also used in urdu. Sheer in persian means milk. When the word is broken up it means one who shares milk with you.
I found this excerpt in, the book ‘Thousand Splendid Suns’ by Khaled Hosseini where the word is used in common parlanceThe scenes following the abortive attempt of Mariam and Laila to leave the country (and their abusive husband) : “What does it matter to you to let a mere two women go? What’s the harm in releasing us? We are not criminals.” “I can’t.” [says the officer who sends them back] “I beg you, please.” “It’s a matter of qanoon, hamshirah, a matter of law. . . . It is my responsibility, you see, to maintain order.” In spite of her distraught state, Laila almost laughed. She was stunned that he’d used that word in the face of all that the Mujahideen factions had done–the murders, the lootings, the rapes, the tortures, the executions, the bombings. . . . “If you send us back,” she said instead, “there is no saying what he will do to us.” She could see the effort it took him to keep his eyes from shifting. “What a man does in his own home is his business.” “What about the law then, Officer Rahman?” Tears of rage stung her eyes. “Will you be there to maintain order?” “As a matter of policy, we do not interfere with private family matters, hamshirah.”
The word ‘Behn’ is also commonly used for sister.