To smoke weed inside a closed environment, such as a car with the windows rolled up. Inhaling the second-hand smoke increases the effect.
We sat in the car and greenhoused a couple of joints.
by Savvy Sin December 08, 2007
To go get stoned/high
"Hey lets go greenhouse" meaning "lets go smoke weed"
by Mac January 15, 2005
RAF wartime slang for Cockpit cover.
"Couldn't get the greenhouse open"
by Gari July 30, 2005