What does sister mean?
A sister is a girl or woman who is a daughter of the same parents as another person. In its most familiar sense, the word names a female sibling and can express affection, closeness, or family connection. It also has several extended uses: a woman belonging to a religious order may be called a sister, women who are close friends may address one another as sisters, and institutions with a shared purpose or structure may describe one another as sister organizations, schools, or companies. The use for institutions is especially familiar in North American English, though it is also understood in British English. As an informal verb, “to sister” means to treat someone with sisterly affection or regard them as a sister. Although its basic meaning remains familial, “sister” thus extends readily beyond a biological relationship to express solidarity, affiliation, and mutual support.
A girl or woman who is a daughter of the same parents as another person; by extension, a female member of a religious order, a close female friend, or a related institution or organization.
"Her sister joined the medical school last autumn."
The familial sense is standard everywhere in modern English. Institutional senses such as “sister city” are especially common in North American usage.
To treat, address, or regard someone as a sister.
"They sister each other throughout the pregnancy."
This is an informal and affectionate use, especially common among women.
The ordinary plural is “sisters.” In religious contexts, “sisters” may refer collectively to women who belong to the same order or community.
"The two sisters greeted us at the entrance."
The word survives from Old English sweostor, a reminder that modern “sister” is a remarkably ancient family word.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does sister come from?
The word descends from Old English sweostor, the inherited Germanic word for a female sibling. It developed through Middle English forms such as suster into modern English sister. Cognates include German Schwester, Dutch zuster, Swedish syster, and Latin soror, all reflecting the same ancient Indo-European family relationship.
Related word forms
How sister is actually used
In its familial sense, the word is standard in British and American English. “Sister” is also used informally as an affectionate form of address. The institutional sense, as in “sister company” or “sister organization,” is especially common in North American English.