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1.
Moom is a word describing a person, object, or animal, that has the appearance of being retarded. It can also be used as a derogatory insult. This was derived from the original Moomin Natalie.

There is also the Moom game, in which each player tries to point out the biggest moom whilst walking along a street.

Moomchild is the expression given to a young moom.
"Your such a moom."

"EUGH! Look, it's a real fuckin' moom!"

"For god sake, Moom is coming tonight as well.
by MoomCat January 02, 2008
 
2.
Stands for "Men's Opposite of Menstruation Syndrome"
A monthly cycle that men go through resulting in moodiness. The emotional male version of a period or PMSing without the physical aspects.
Watch out, Jim is on his MOOMS
by Bugmenot123123123 November 07, 2007
 
3.
to be slightly saddened when you hear or experience something that you do not like or that has otherwise make you feel unhappy in some way.
georgina: "how am i smelling today"

peter: "not so fresh"

georgina: "ow moom"
by Mezzaj January 24, 2012
 
4.
To kill someone in an unforgiving way in Call of Duty.
Dude, I just moomed you!

Get Moomed!
by Moomer September 07, 2011
 
5.
Verb- describes the act of eating an uncooked egg off your own breast.
"Billie is such a tramp. I went to a party at her house the other week and she ended up sat there mooming with loads of guys jerking off around her"
by calicojack May 20, 2009
 
6.
1) 'Everything', It is used to confuse others. (n)

2) A rubber blue cow, which was beheaded. (n)
1) "What is Moom!" -- "It is everything *walks away*"

2) Moom has no head.
by ben February 08, 2004
 
7.
The act of being lazy. A "moomey-like" approach to life.
I'm really tired, I think I'm just going to moom out for awhile.

Where is Kyle? Oh hes just moomin out on his couch.
by Derelicte25 April 10, 2008