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1.
A term used to denote one's intention of smoking weed before an activity or attending a public event. It may also imply that the smoking takes place in an enclosed area.
Hey, do you wanna preheat before we go see Alice in Wonderland?
by crazynorw3gian December 07, 2010
 
2.
stocking the pantry full of munchies prior to getting "baked." (high as fuck).
larry: dude i got this new piece today, since it's 4/20. wanna go try it out?

andrew melvin: yeah man but did you pre-heat the oven?

larry: helllll yeah, niggy. i got captain crunch, chips ahoy, cheetos, peanut butter and all day hawaiin punch.
by Ryan Harrison April 19, 2011