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1.
1D
The abbreviated name of boyband One Direction. They placed third in the seventh series of The X Factor UK.

Predicted by industry experts as Britain's next big boyband, they have ignited hysteria across the country. Their book, "Forever Young: Our Official X Factor Story" has reached the number one spot on the Sunday Times Bestseller list.
Dannii: Have you been to the X Factor Tour? How was it?

Simon: Yes. It was great. 1D stole the show! They received the biggest cheers and had the most amount of merchandise on sale. They should just rename it the One Direction Tour.

Dannii: Matt Cardle's fans must be fuming with jealousy, huh?

Simon: 1D are the real winners of the X Factor. Everyone knows it.
by ProbablyBlue March 09, 2011
 
2.
1d
to fight someone one on one. usually people say 1d, but it really turns out to be a fight dealing with more people.
yo ima 1d that herb son
by fighting for survival August 08, 2005
 
3.
1d
Within the Counter-Strike gaming community, "1d" is used as both a noun and a verb to describe a head-shot kill while using the Desert Eagle with only one bullet fired at the enemy. It is considered a demonstration of skill in the game.
noun: "kx just got a 1d again."
verb: "willow was 1d'd."
by kx October 23, 2012
 
4.
1D
this or that, left or right, black or white, one way or the other.

a new way to say any of theese words, its !D because just like in an old school arcade game, you are limited two just two directions of movement. Like in a real life situation court, either you killed the guy or you didnt, no i was acting on another influence crap.
Lawyer: did you rape that woman jason?

jason: well..... you know it was, a yeah, ahh.

lawyer: its a 1D jason

reporter: did you know 911 was going to occur before it happened.

gov. offical: we did everything in our power to save 911 victims.

repoter: it's a 1D question jackass, don;t go giving me that shit
by CREEDS January 19, 2010
 
5.
1'd
verb: gave a rating of "1"(out of some number) to something.
Used to indicate major suckage or disapproval.

The opposite might be "5'd" or "10'd" if the maximum possible rating was, respectively, 5/5 or 10/10.
Often seen in reference to a YTMND animation/page, where users are encourage to rate YTMND creations on a scale of 1-5 stars:
"That was totally lame.. I just 1'd it".
by Belge January 30, 2006
 
6.
1D
Noun. Refers to a women's chest that is so flat when you get your level out and put it on their chest it is perfectly level.
That chicks face is alright, but her chest is 1D.
by Brett Costello April 03, 2005