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1.
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
 
2.
To go get stoned/high
"Hey lets go greenhouse" meaning "lets go smoke weed"
by Mac January 15, 2005
 
3.
RAF wartime slang for Cockpit cover.
"Couldn't get the greenhouse open"
by Gari July 30, 2005
 
4.
the bank
I went to the greenhouse to cash my government check.
by bearsfan23 August 04, 2010