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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 12, 2005
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2
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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4
Short for sister, commonly used as a term of endearment to friends in urban new york/jersey areas
by Caroline Might Fine November 14, 2016
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5
1.) A South African English expression roughly equivalent to the American "yech" and the Afrikaans expression "sies".

2.) An American term of endearment for a sister, now also used in other countries.
1.) Sis, man, you stink!

2.) Hey, sis, hey bro, how's Ma doin'?
by Xaviana December 01, 2003
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6
SiS as in Shit Its Sunday Commonly used on sites like Facebook and Myspace
John: Aw man SiS
Kevin: Dude I know
by Kife1100 April 05, 2009
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7
Snickering in Silence
new for LOL because it applies much more than LOL when texting/typing and trying to be quite
While texting in class i received a message with a prime time to say "thats what she said" and/or "reminds me of my saturday night" or even "I get that all the time" so I sis'd vs lol'ing

"idk what happened it just went everywhere after i touched it"
sis
"reminds me of my saturday night"
by kevin "k-bone" December 25, 2009
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