noun

• (British) A senior or supervisory nurse, often in a hospital.
• (African-American Vernacular, slang, sometimes capitalized) A black woman.
  "A fly sister rolled in with a suitcase full of hip-hop novels called The Glamorous Life, and an African brother with long dreads wanted to sell them some incense and some fake Jacob watches."
• (informal) A form of address to a woman.
  "What’s up, sister?"
• (attributively) An entity that has a special or affectionate, non-hierarchical relationship with another.
  "sister publication"

verb

• (transitive, construction) To strengthen (a supporting beam) by fastening a second beam alongside it.
  "I’m trying to correct my sagging floor by sistering the joists."
• (obsolete, transitive) To be sister to; to resemble closely.
  "Deep clerks she dumbs; and with her needle composes Nature's own shape, of bud, bird, branch, or berry, That even her art sisters the natural roses; Her inkle, silk, twin with the rubied cherry"