Entries linking to sea-green
Old English sæ "sheet of water, sea, lake, pool," from Proto-Germanic *saiwa- (source also of Old Saxon seo, Old Frisian se, Middle Dutch see, Swedish sjö), of unknown origin, outside connections "wholly doubtful" [Buck]. Meaning "large quantity" (of anything) is from c. 1200.
Germanic languages also use the general Indo-European word (represented by English mere (n.1)), but have no firm distinction between "sea" and "lake," either by size, by inland or open, or by salt vs. fresh. This may reflect the Baltic geography where the languages are thought to have originated. The two words are used more or less interchangeably in Germanic, and exist in opposite senses (such as Gothic saiws "lake, marshland," marei "sea;" but Dutch zee "sea," meer "lake"). Compare also Old Norse sær "sea," but Danish sø, usually "lake" but "sea" in phrases. German See is "sea" (fem.) or "lake" (masc.).
Boutkan writes that the sea words in Germanic likely were originally "lake," and the older word for "sea" is represented by haff. The single Old English word sæ glosses Latin mare, aequor, pontus, pelagus, and marmor.
Meaning "dark area of the moon's surface" is attested from 1660s (see mare (n.2)). Phrase sea change "transformation," literally "a change wrought by the sea," is attested from 1610, first in Shakespeare ("The Tempest," I.ii). Sea anemone is from 1742; sea legs, humorous colloquial term implying ability to walk on a ship's deck when she is pitching or rolling is from 1712; sea level from 1806; sea urchin from 1590s. At sea in the figurative sense of "perplexed" is attested from 1768, from literal sense of "out of sight of land" (c. 1300).
Old English grene, Northumbrian groene "green, of the color of living plants," in reference to plants, "growing, living, vigorous," also figurative, of a plant, "freshly cut," of wood, "unseasoned" earlier groeni, from Proto-Germanic *grōni- (source also of Old Saxon grani, Old Frisian grene, Old Norse grænn, Danish grøn, Dutch groen, Old High German gruoni, German grün), from PIE root *ghre- "grow" (see grass), through sense of "color of growing plants."
From c. 1200 as "covered with grass or foliage." From early 14c. of fruit or vegetables, "unripe, immature;" and of persons, "of tender age, youthful, immature, inexperienced;" hence "gullible, immature with regard to judgment" (c. 1600). From mid-13c. in reference to the skin or complexion of one sick.
Green cheese originally was that which is new or fresh (late 14c.), later with reference to coloring; for the story told to children that the moon is made of it, see cheese (n.1). Green light in figurative sense of "permission" is from 1937 (green and red as signals on railways first attested 1883, as nighttime substitutes for semaphore flags). Green thumb for "natural for gardening" is by 1938. Green beret originally "British commando" is from 1949. Greenroom (also green room) "room for actors when not on stage" is from 1701; presumably a once-well-known one was painted green. The color of environmentalism since 1971.