The term sister
is often used in Ancient Near Eastern love poetry as a term of endearment. It indicates that the bond of companionship in their relationship is like that between a brother and a sister, the closest bond of friendship that was possible with a person of the opposite gender. In the same way the woman will wish that the young man were her brother so that she could openly display her love for him (Song of Solomon 8:1). Their sexual union is a union of body and soul in which two people are united in every aspect of their lives.1
9 Tu me ravis le cœur, ma sœur, ma fiancée, Tu me ravis le cœur par l'un de tes regards, Par l'un des colliers de ton cou.