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1.
A combination of slutty or sensual kisses. Origin author Caden Leigh.
She gave sisses on her way out of the room.
by Sisses January 04, 2010
 
2.
To sit and piss, generally by a male.
"I went to siss before going out drinking." "I was sissing when you called."
by Antarctic December 18, 2009
 
3.
Sudden Ice Shift Syndrome. An event that sometimes occurs when a person is drinking a beverage containing ice. As a container is tipped up to pour the liquid into the mouth, a mass of ice, formerly lodged near the bottom of the container, shifts under the force of gravity, causing the beverage to spill down the chin of the drinker. This phenominon is not observed when drinking through a straw.
As he mopped the stain on the front of his shirt, the young man who had just tried to pour the last of his long island iced tea into his mouth exclaimed "SISS!" (pronouncing the acronym S.I.S.S.)
by Dale Seng November 23, 2006
 
4.
Standard Issue Street Soldier
Police, Sheriff or any law enforcement officer

A couple S.I.S.S. chased me over a couple fences.
by JAE26 March 22, 2007