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A best friend that you can call sis-sis instead of sis. Female version of brobro. Guys can have a best friend that is a girl that you can call sis-sis and nothing is going on or no one is going out.. Normally if you are best friends you can treat her like a real sister. You can love her like a real sister say I love you like you say to a real sister. Basically best friends.
Jason: Wow Chelsea, we have been friends for years now and I proud to call you my sis-sis.

Chelsea: Thanks Jason! Can I call you brobro?

Jason: Sure sis-sis.

Chelsea: Love ya brobro.

Jason: Love ya sis-sis.
by Thekidwhoisakidthatgoestomps January 25, 2011
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