SiS

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 5, 2009

SI

SI is the abbr. of stupid idiot , although it can also be used in a way in which it means mug

I.E. billy you fucking si, si does not mean sigh which means you bore.

by jake lowe February 11, 2008

SIS

Smirk in Silence:
The act of putting on a straight face after putting someone in a spot.
Pulling someone's leg as a group where everyone acts normal in a scenario that is funny.
Used on social networks, chat rooms and forums..at least could be!

Totally loved getting on Spook's nerves acting as if I don't know him at the bar last night. Pulled a SIS.

by far_c November 2, 2009

SIS

suck it slow

i want you to SIS

by foonster March 8, 2010

sis

stay in school, from peaches song "fuck the pain away"

sis iud stay in school cuz it's the best

by peter brook August 2, 2008

SI

A term often used when talking about mental health treatment meaning suicidal ideation or suicidal thoughts

My SI had been chilling lately

by Bitchbotch June 22, 2019

SI

Sisteme Internacional

SI units are the best, man. Inches suck.

by AnActualDefinition March 12, 2018