A term often used by males to describe their relationship with a girl who is not their girlfriend, but a close friend. This term does not apply to blood-relatives.

This classification boasts qualities typically seen in brother/sister relationships (e.g., mildly derogatory dialogue, occasional use of derogatory hand gestures, random story telling and re-telling, matchmaking, inside jokes, mutual-aid and support related to interference by outside parties, and the occasional transfer of funds with no repayment plan).
Person 1: "Did you see how fat so-in-so has gotten?"
Person 2: "Hey, watch your face, that's my fake sister you're talking about."

Person 1: "So-in-so said you loaned her $200"
Person 2: "Yeah, it's ok. She's my fake sister. I'll hit her up for $400 next time."
by wordalicious December 8, 2010
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December 5 is the day you should say your fake sister and if y’all like it then y’all should date fake sister or fake brother go for it ! I mean try summ new!!
by Lowkeykeen December 5, 2020
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December 5th national date your fake sister or fake brother for a day no regrets you have to date them no cheating
“It’s December 5 yo why be single” or “it’s national date your fake sister day let’s go”
by Lowkeykeen December 5, 2020
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