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."
