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1. (n) A sample of human excrement which is so large in physical volume that a sense of alarm is immediately raised as it is commonly mistaken to be the size of the now extinct animal, Elephas americanus; colloquially referred to as the "Mastodon"

2. (n) A shit so absolutely anus-tearingly huge that you'd fucking think it's a real life mastodon erupting from your rectum.
Bob: Dude I just dropped a huge fucking mastodeuce in my ex-girlfriend's toilet and it won't fucking flush. LOL!

Jeff: Nice fucking work dude. You should blame it on her mom.
by EarlUxbridge August 21, 2014
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