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1.
Just like the word serious but more seriousness. Usually used by the more popular kids at school.
Dude I'm Cerial I really did it with Carmen Electra.
by John Greg September 29, 2007
 
2.
An adjective to describe someone who not only looks and acts like a serial killer, but also exhibits qualities of a cereal like nature.
"Omg! Look! It's that cerial kid! He totally looks like he is going to hurt someone!"
by Mr. Bleil April 23, 2008