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2.
Serious as Sirius Black.
Person 1: "Is Sirius siriusly dead?"
Person 2: "Ya, totes."
by Calloway April 13, 2006
 
1.
Something you say when what you are talking about is so serious, it's gone Sirius Black serious.
"You're joking, right?"
"No, dude. I am not. Siriusly."
by Gennnnn March 15, 2008