1) Short for sister
2) In the song Fuck the Pain Away by Peaches, SIS seems to stand for Stay In School...
My sis went to the movies with a scumball.

"Stay in school... Cause it's the best..."
by wxynot July 13, 2005
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Abbreviation for: "Sisters, In, Spirit". Your Best Friend or Bae. Usually used to refer to someone really close to you, someone you spend a lot of time with, like your sister.
Girl: OMG, squad on fleek!
Girl 2: yas, we look #Fabulous
Girl: Yas Sis Yas!
by ChocolateWafflez April 15, 2015
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Abbr. for 'stupid idiot'
As in Football Factory from 2004:
"Jog on, you si!"
by Nige Menzel May 24, 2007
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the abbreviation of "sister";
a genderless term much like "bro" or "dude"

people can also say it like "sister" but that doesn't change the definition

like when you say "brother" instead of "bro"
-"How do you feel about celebrity drama?"
-"It's the tea, sis."

-"Hey sisters!" -James Charles

-"How u doing?"
-"I'm so fucking depressed, sister"
by Bakuhoe Katsubitch January 10, 2019
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Suffix added to the end of almost every word. Used mostly by 40 year women talking to their children and/or dogs, or drunken college whores in a desperate attempt to sound more cute, less riddled with STDs and premature, substance induced age.
Ok, who wants napies?

Who's got tired little legsies?
by Ihateyouallsomuch July 8, 2005
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