Definition of: sister

(sis′tər) noun
1. A female person or animal having the same parent or parents as another person or animal. Daughters of the same parents are full or whole sisters, called in law sisters german. Those having only one parent in common are half–sisters.
2. A woman or girl allied to another or others by some association: sisters in spirit: also used figuratively: Astronomy and astrology are sisters.
3. Eccl. A member of a sisterhood; a nun.
4. A head nurse in the ward of a hospital; also, popularly, any nurse.
—the three (or Fatal) Sisters The Fates.
—adjective Bearing the relationship of a sister or one suggestive of sisterhood. [<ON systir]
—sis′ter·ly adjective