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1.
green-top
-noun

1. the act of taking the first hit off a freshly packed bowl of unburned cannabis flower (weed), in which case the smoker experiences maximum flavor potential. Right of the said act is considered to be inherited by the owner of the weed, although sometimes it is bestowed to another smoking participant.
Nah Shane, I had greentop last time; now It's your turn.
by Doc J and Eightball November 10, 2011
 
2.
the first hit of a packed bowl of weed.
When smoking weed in a group it's always best to get green top because that's the best hit.
by BuzzOnBuzzOff October 06, 2009