look up any word, like darude - sandstorm:
 
1.
someone who has sex his girlfriend and then break up with her.
"I had sex with Emma yesterday." "Awesome! you gonna marry her?" "nah..i'm gonna break up with her." "omg, you're such a Niels."
by Bantumie September 14, 2009
 
2.
Someone with a narcist-complex that will write everywhere what a god he is. While actually he resembles an old shoe, is utterly pathetic and has no real skills whatsoever. Rather is chating the most hidious girls up than spending time with his family. The ultimate loser you will ever meet.
A girl comes up ignoring Niels

Niels: It's obvious, she wants me so badly. She loves me so and everything she does and will ever do in her life she will do it for me.

Niels friend: I know (you think) you're fantastic but isn't it time for you to go home for your dinner now?
by tdrqc September 17, 2013
 
3.
hottness; gorgeous; an immensely talented person; adored; unique. This stems from the name nathaniel which means gift from god, or God's gift. This is the name of a very cool and mature guy I know.

Nelsity (noun)
The nelsity of that girl is undeniable.

DAMN! He is niel!

Another niel in the making.

Wow, that kid is soooooo niel; just look at him!
by Ex- ByFid April 12, 2005
 
4.
Niels Henrik David Bohr: 7 October 1885 – 18 November 1962) was a Danish physicist who made fundamental contributions to understanding atomic structure and quantum mechanics, for which he received the Nobel Prize in Physics in 1922. Bohr mentored and collaborated with many of the top physicists of the century at his institute in Copenhagen. He was part of a team of physicists working on the Manhattan Project

Another definition of this word: champion.
Wow that person is a real niels
by John Martyr September 25, 2010
 
5.
Someone while under the influence of marijuana runs away from cops at great speeds. If a cop is spotted 50 yards away from them arresting someone else, they decide to sprint away.
Reilly: hey look theres a cop down near rite aid.

Niels: fuck!!!!!!!!!!!

Dain:Where did niels go?

By this time niels is about 50 ft away running 20 mph.
by Therealistkillaz December 12, 2011
 
6.
The most horribly smell ever. It looks like a pig pile of shit and it smells horribly.
Oh dude just had the most amazing niels ever.
by Jemoederniels July 19, 2010
 
7.
A slang, or "street-name", for the wonderful drug MDMA (Methylendioxymethamfetamin) which is said to contain bits of real panther. When this "drug" is taken, one experiences a euphoric high while simultaneously boosting ones showmac skillz x 100000000!
HV på Niels i går!
Har du noget Niels?
Skal vi være sammen med Niels i dag?
Niels er min bedste ven.
Niels conquers all <3
by MathiasSander January 10, 2012