Top Definition
The last evolution of the grass type starter Pokemon in Pokemon Gold/Silver/Crystal/HeartGold/SoulSilver. Evolved from Bayleef, which was evolved from Chikorita. It can revive dead plants back to life with its breath.
Person 1: Hey, what starter Pokemon did you chose in HeartGold?
Person 2: I chose a Chikorita! It's already a Meganium! :D
by LevanJess April 24, 2011
1 more definition
extremly large, king size penis.
"whoa! hakko you didnt tell me you weilded a meganium!?" - suckyfucker Mclickerson
by Hakko November 21, 2004

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