stands for self-injury. Aka cutting, burning, etc. for emotional distress reasons
Person 1- Did you SI today?

Person 2- I haven't hurt myself on purpose in like a week.
by Injuried November 07, 2010
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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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a genderless term much like "bro" or "dude"

you don’t have to be BFFS. You don’t really even have to know them. If she seem chill. then SISSSSSS is what they should be called!
JACK: *texts Jill*

“ SIS! You’ll never believe what popped up on Greg’s phone!!”

Jill: “Girl, SPILL!”

Jack: “Some HOE’S NAME! Do you think he is cheating on me?!”

Jill: “ SIS! YES! Leave his ass!”

****you can also use it in less dramatic scenarios****
by URB@NL3GEND March 04, 2020
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Short for "System International." Also known as the Metric System.
The SI system makes more sense than the English system. It should be officially adopted by the US, but we Americans are too lazy for change.
by BlastMaster June 12, 2003
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Its a model of faster model of the Honda Civic, meaning "Sport Injection"
My civic DX got spanked by that Si hatck.
or
Im bout to get me some Si rimz dawg.
by Tsugaru November 26, 2003
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