Definition of greenies:
(n) :
(chiefly Australia, New Zealand, slang, derogatory) An environmentalist, someone who shows concern for the environment; often aimed at environmental extremists.
(n) :
(Australian politics, informal, by extension) A member of the Australian Greens.
(n) :
(US, slang) A beginner, a novice; a greenhorn.
(n) :
(informal) An unripe fruit.
(n) :
(US, Wyoming, derogatory, slang) A person from Colorado; after the color of the Colorado license plate.
(n) :
(slang) A blob of nasal mucus; a bogey.