Your sister is your female sibling. If your parents have six children, and all of them are girls, that means you have five sisters.
Your biological sister has the same mother and father that you have, but some sisters are adopted, or even have a different mom or dad (some people call this a stepsister or a half-sister). If you join a college sorority or a trade union, you’ll refer to the other members as your sisters. Catholic nuns and other religious women are also called sisters. The roots of sister go back to words meaning “one’s own” and “woman.”
a female person who has the same parents as another person“my
sister married a musician”
a female person who is a fellow member of a sorority or labor union or other group“none of her
sisters would betray her”see more
(Roman Catholic Church) a member of a lay sisterhood (one of several founded in the Netherlands in the 12th and 13th centuries); though not taking religious vows the sisters followed an austere life
(slang) sometimes used as a term of address for attractive young women