ONS is an acronym indicating the common dating phenomenon One Night Stand. You can use the acronym ONS to indicate a person with whom you have had said One Night Stand.
You: "Uh-oh, guess who just walked in?"
Me: "Shit. Who?!"
You: "ONS"
Me: "Great... and I thought I'd never have to see him again."
by Roberta Pincer April 11, 2005
This stands for "One-Night-Stand" and is used by some males to inform thier friends what they think of certain women in the club.
Check her out!! She is definately an ONS I wouldnt mind havin tonite!
by Shinshoryuken January 14, 2006
Onslaught, a game mode in Unreal Tournament 2004 where players trying to capture nodes to eventually make way to the enemy base and try to destroy the power core.
It takes good team strats to win at ONS.
by CorporationX February 18, 2005
ONS is an abbreviation for "Over Night Studying", SON can also be used in some occasions. It is an action held by most, if not all, petroleum engineering students. It has been well known through out time, that this habit is to be practiced before major exams, and even quizes. According to new Petroleum engineering students, ONS is a sacred retual, that every -successful to be- engineer should experience!
"Normal student Helal" : Ughh, Got a midterm tomorrow, ONS :D ??

2 years later..

"ADMA executive manager HaLool :3" : SON was worth it alright :3!
by Hallulz November 20, 2010
An informal code of street fighting, not allowing bystanders to interfere in the fight.
Hey bitch-ass, let's square it up one-on-one in the midldle of the street!
by PGrace August 5, 2003
a bag of heroin and coke together.
i wanted to do a speedball so i told my connect i need a "one and one" bag.
by fresh stallion April 12, 2010