'Half brother' in the Bible

It happened afterwards that Absalom the son of David had a beautiful sister whose name was Tamar, and Amnon [her half brother] the son of David was in love with her.

He said to Amnon, “Why are you, the king’s son, so depressed morning after morning? Will you not tell me?” And Amnon said to him, “I am in love with Tamar, my [half-] brother Absalom’s sister.”

Later, her brother Absalom asked her, "Has Amnon, that brother of yours, raped you? Then keep quiet about your half-brother for now, my sister. Stop taking this so personally." From that time on, Tamar lived in continuous desolation within her brother Absalom's house.