The term sister comes from Old Norse systir which itself derives from Proto-Germanic *swestēr, both of whom have the same meaning, i.e. sister. Some studies have found that sisters display more traits indicating jealousy around their siblings than their male counterparts, brothers. In some cultures, sisters are afforded a role of being under the protection by male siblings, especially older brothers from issues ranging from bullies or sexual advances by womanizers.
^Volling, B. L.; McElwain, N.L.; Miller, A.L. (2002). "Emotion Regulation in Context: The Jealousy Complex between Young Siblings and its Relations with Child and Family Characteristics". Child Development 73 (2): 581–600.
^Handbook of Cultural Psychiatry - Page 67, Wen-Shing Tseng - 2001