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3.
adj: an all purpose word for something cool, hip, or awesome; or evil, twisted, and sick. Also functions well as a nickname.
Example of cool: Dude, Lord of the Rings: ROTK was SO pernicious!

Example of evil: Our algebra homework last night was PERNICIOUS! I didn't get any sleep!
by Niph April 24, 2004
 
1.
adj. causing great harm, or death, or something else real bad.
DAMN that was a pernicious fart.
by Emetic August 28, 2003
 
2.
Describes something that really messes you up. Most of the time you can't tell at the beginning but before you know it, it really fucks you up.
Person 1: It ain't worth it bro, you know Prozac is pernicious. Don't take it.

Person 2: Too late, I can't get off of it now.

Person 1: Damn, I hope you don't get erectile dysfunction like that other kid.

Person 2: Too late for that too...
by Moses D. October 07, 2011
 
4.
The best type of deed!
Freyalise set up us the bomb; Yawgmoth will pay for his treachery; Freyalise performed her pernicious deed.
by The Ravenclaw Seeker April 27, 2004