The amalgamation of "masterpiece" and "ass" - essentially a masterful ass. This is applicable to any female that has a lot to bare with her derrière.
Jessica Biel has an ass that won't stop! What an assterpiece!

Even in her older state, J Lo still has a mighty fine assterpiece protecting her backside.
by JDMGio January 28, 2011
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the wonderful paintjob that one gives the toilet when they have explosive diarreah
I painted such an assterpiece today that I thought I was Michaelangelo.
by Johnny Tats December 10, 2007
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