The origin is from the noun, mercenary. A mercenary is someone who will carry out combat missions but aren't part of an official organization, like the military, or CIA and are usually not motivated by justice or an allegiance. (They are usually motivated by profit) Activities associated with these "rogue agents" or "guns for hire" usually involve violence, and often killing.

So the slang verb "merc" generally means to perpetrate violence, usually killing, but can just mean to beat someone up (usually to teach them a lesson/send a message). Or it can be used figuratively, as in, "that mc just got straight merc'd in that rap battle". Similar figurative expressions could be, "Man, he just got smoked!", "Dude, you totally slaughtered that guy", "Yo, she schooled that chick", "When my boy rocks the mic, he be killin' any sucka mc that steps to him".

Like many slang terms, there is an original way to spell it and variations on spelling that can become widely accepted (it is slang after all, so normal grammar rules do not necessarily apply). Merc is the origin spelling, whereas murc, murk, merk, etc are alternates. Like some people write murda instead of murder, dood instead of dude, or dat instead of that.
"You mess with my girl again and I'll merc your ass."

"We totally merc'd the other team in COD last night."

"A guy walked in with a gun and just started mercin' people left and right."

"I heard those old school mobsters would merc somebody just for looking at them the wrong way"

"Yo, I was spittin' rhymes in this cipher last night and this whack mc stepped to me, but I straight merc'd dat foo."
by mockarena July 17, 2014
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To fuck a person up real bad or kill them in a ruthless manner
I am going to merc that nigga who talking that shit.
by Maurice November 15, 2003
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Land of the Doint, Dointest, A place where the weather is far from temperate, the smell of cattle and agricultural waste sting the nostrils. The landscape is far from interesting and can best be described as Sandy Mush. Other then the Incomplete Uc campus the area can be deemed a technological black whole lacking anykind of service minimize contact to the outside world and confining those with to their own weirdness. Only means for survival in such a living situation is to peridica;;y escape.
"Last time I woke up in merced i thought I was still dreaming"

"Don't take acid just go to merced"
by mercedkilla September 21, 2011
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the backwater town of California, and the only city that has a UC and can still boast that citizens can go anywhere in town and know at least ten people there. Filled with baby boomers whose own parents are from the hick parts of the east coast, the schools may be filled to the brim, but do not be fooled: if there ever was a cliche "country" town in california, this is it.
"You know, when you're drunk you kind of have a Southern accent."

"Well, I'm from Merced."

"Oh. That makes sense, then."
by Rose Saratoga April 03, 2009
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Originated from the phrase "lord have mercy!" when uttered on sight of a beautiful woman, meaning sexually attractive or a girl who is sexy.
1. "Beyonce is so merce!"
2. "check that merce out, I'd love to spaff up her nose"
by Tony Bones April 20, 2005
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A semi-famous gaming clan that has played multiple MMOs (such as UO and Darkfall Online). They are a bunch of power gamer scrubs who will power grind their characters to the max, dominate everyone else with said characters, then proceed to claim victory and quit the game before everyone else has a chance to catch up. They suck in FPS games in which character development is not a factor, and will continue to bare the biggest undeserved egos in the history of gaming clans. If you encounter a merc outside of an MMO, rest assured that you can, and you will, shit on him.
Osium from The Mercs is a scrubby douchebag, but when you challenge him to a fight he redirects you to his peons to fight for him. He does all the shit talking though.
by Osium Woof July 06, 2010
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