A girl or woman who shares a common ancestry, allegiance, character, or purpose with another or others, specifically, Informal Used as a form of address for a woman or girl, One identified as female and closely related to another, adjective_ Related by or as if by sisterhood; closely related, Genetics Of or being one of an identical, related, or homologous pair, verb_ obsolete, transitive To be sister to; to resemble closely, transitive, construction To strengthen (a supporting beam) by fastening a second beam alongside it