Definition from Wiktionary, the free dictionary
From the plural form of green.
- Plural form of green
- (plural only) The leaves of certain edible green plants, especially of brassicas, eaten as a vegetable.
- (plural only) Any vegetables eaten by humans, regardless of colour.
Derived terms 
- beet greens
- collard greens
- dandelion greens
- mess of greens
- salad greens
- spring greens
- turnip greens
- warrigal greens
leaves of certain edible green plants
any vegetable eaten by humans, regardless of colour
- Third-person singular simple present indicative form of green.