For Def Sure Share definition Flag When simply saying 'yes' just isn't good enough. It's like saying yes, but X10. Usually used with an exclamation point Kat: I'm so hungry Reuben: Do you wanna get some Chinese food? Kat: For def sure! For Def Sure by Kitty Kat Wants Your Soul March 30, 2008 Get the For Def Sure mug.