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1.
Inserting a penis into a girls mouth while on all fours.
Her four limbs in conjunction with your four limbs create the spiderhead effect.
by Arachnophobia January 31, 2010
 
2.
First mentioned in the Bass Millionaire song, "Smokin' Indians," spider head means when one receives oral sex from eight different partners at the same time.
They just gave me spider head in my bed!
by Bass Kid March 30, 2011