Greens

wiktionary

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From Middle English grenes, equivalent to green +‎ -s. Compare Saterland Frisian Gräinieten(“vegetable”), West Frisian grienten(“vegetables, greens”), Dutch groenten(“vegetables, greens”), German Low German Gröönten(“vegetables, greens”), Danish grøntsager(“vegetables”), Swedish grönsaker(“vegetables”).

From green(verb).

etymonline

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greens (n.)

c. 1400, "vegetables;" 1690s, "freshly cut branches used for decoration," from green (n.). Meaning "ecology political party" first recorded 1978, from German die Grünen (West Germany), an outgrowth of Grüne Aktion Zukunft "Green Campaign for the Future," a mainly anti-nuclear power movement, and/or grüne Listen "green lists" (of environmental candidates). Green (adj.) in the sense of "environmental" is attested in English from 1971; Greenpeace, the international conservation and environmental protection group, is from 1971.