1. (

• sister ,
• sis

) a female person who has the same parents as another person; "my sister married a musician" ;

2. (

• Sister ,

) (Roman Catholic Church) a title given to a nun (and used as a form of address); "the Sisters taught her to love God" ;

3. (

• sister ,

) a female person who is a fellow member of a sorority or labor union or other group; "none of her sisters would betray her" ;