Noun- A hypothetical dinosaur large enough to swallow the sun. Also possibly the pet of Galactus.
1- "What happened to the sun, dude?"
"Oh, Galactasaurus Rex ate it."

2- "Yo, Andrew, what happens to planetary nebulas at the end of the Hertzsprung-Russell cycle?"
"I eat them. For I am Galactasaurus Rex. Muahahahahhahahaha!"
by Manish Melwani May 8, 2008
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