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 09, 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 08, 2005
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Dialect of UnaRocks added to the end of various words for no particular reason.

'Sies disease' is the propensity to become addicted to the suffix 'sies'
That car is awesome, wantsies!

I'm so hungoversies today

Would you like to go for some drinksies this evening?

I have the sies disease so badsies
by UnaRocks December 13, 2007
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Abbr. for "self-injury," also known as self-mutilation. Most common form is cutting, but may also include burning, bruising, skin-picking (excoriation), and other behaviors. There is no single cause for SI. SI is most common in women and tends to persist for years.
As a result of overwhelming anxiety, she turned to SI as a coping mechanism.
by rieux November 27, 2003
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