Short for Master Chief Petty Officer. The Master Chief Petty Officer is the ninth, and highest, enlisted rank in the U.S. Navy, just above Senior Chief Petty Officer, and is a non-commissioned officer. They are referred to as Master Chief in most circumstances.

Advancement to Master Chief Petty Officer is similar to that of Chief Petty Officer and Senior Chief Petty Officer. It carries requirements of time in service, superior evaluation scores, specialty examinations, and peer review. A Senior Chief Petty Officer can only advance if the existing master chiefs approve.

A Master Chief Petty Officer is purely administrative and is usually tied closely with the Commanding Officer, except possibly when the command is very large (e.g. an aircraft carrier). Their uniform reflects this administrative duty; becoming similar to that of an officer, albeit with different insignia than an officer.
The master chief came down here and busted those guys asses for being drunk on board ship.
by jt October 17, 2004
a boy portraying the character off of the halo trilogy. this boy portrays master chief only when he is in the act of the giant circle.
"Master chief what is taking so long?!?!?!"
"I'm loading my plasma grenade if you know what i mean."
"Ooooh you a kinky bitch master chief"
by Banana Hamikk May 10, 2008
A euphenism for a penis.
If you'll excuse me, I think I need to go run Mater Chief through some drills.
by fakemonster July 27, 2005
A 7'1" tall genetically alterred soldier in the video game called Halo, who fights off aliens, and masturbates to a hott computer AI called Cortana who wishes she was a real person so she could ride his cock, while master chief wants to have little computer babies with her.
im tha master chief bitch! ride my cock you filthy computer whore! lawl!
by blahhomies September 10, 2006
some kick-ass soldier of an awsome game which is awsome and yeah ummm... i like penguins! and he is a kick-asser of super assers in the fucked up galaxy we like in! Masterchief rox but his lesbo pal named cortona is well a lesbo and sucks other lesbos boobs.
master chief what a sexy beast of a soldier!
by walmer April 18, 2005
a faggot guy wearing a green costume. Everything is fake and all u losers out there obsesed with the game just face it, hes a faggot! he has a girlfriend who isnt even real, named cortana, who lives in his head! He's a fag.
Hey did u just see the pictures of the Master chief i took with him having sex with cortana?!?!?!?!
by walmer March 07, 2005
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