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

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The most amazing soldier in all of history. As a Spartan II, he was trained to be the best soldier ever. He has saved thousands of galaxies and planets, and is definitely better than Spartacus, pie, the muffin man, and cute puppies. Do not anger his epicness.
Master Chief: Hey ladies, I just got back from saving the universe.

Ladies: OMFG!!!!! SIGN OUR BODIES IN PERMANENT MARKER!!!!!!!!
by The God of Halo 4 December 27, 2012

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A heavy smoker, able to hit and clear a bong all at once.
I am Master Chief!
by Loganbuuullshit October 20, 2010

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Playing Halo, getting a blowjob, while smoking a blunt.
Dude, last night my girlfriend surprised me with a Master Chief.
by M3TALxSLUG August 23, 2012

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The best most badass soldier ever created and also can take on a legion of (grunts) (jackals) and (elites) by himself
MASTER CHIEF is so badass
by MASTER CHIEF 117 November 18, 2016

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-noun

1. a masturbatory handkerchief.
Cheech: Hey man, you should light that subpoena up, dude.
Chong: No man, I'm gonna use it as a Master Chief.
by Urbanium January 19, 2010

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To smoke Weed namely Dank
Man I was so messed up, I was master Chiefed!
by gonzominium July 05, 2009

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the man who gave Hitler the idea to start his own genocide
Hitler-"I see that Master chief can kill an entire race, I bet I can to and get away with it! its brilliant!"
by Th3on3andonlylov3r March 25, 2011

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