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1.
Derived from the word Doppelganger, an Oppelganger is your doppelganger of the opposite sex.
Guy: If I was a chick, Reese Witherspoon would be my doppelganger.
Girl: Reese Witherspoon is totes your oppelganger.
by Elbo December 28, 2012
 
2.
someone who is seemingly just like you but on closer look is, in fact, your opposite.
My two blonde friends are oppelgangers--they're both blonde and have the same job, but one is a badass dry-witted sports nut, and the other is a fashion- and boy-obsessed neurotic.
by katewoo October 20, 2010