Definition of blood sister in English:

blood sister

noun

  • 1A woman or girl who shares at least one birth parent with another person; a sister by birth.

  • 2A woman or girl who has pledged to treat another with loyalty or trust, typically in a ceremony involving the mingling of blood; a trusted friend or companion.

Origin

Mid 19th century; earliest use found in Church Review. From blood + sister.

Pronunciation

blood sister

/ˈblʌd sɪstə/