- sea (n.)
- Old English sæ "sheet of water, sea, lake," from Proto-Germanic *saiwaz (cf. Old Saxon seo, Old Frisian se, Middle Dutch see), of unknown origin, outside connections "wholly doubtful" [Buck]. Germanic languages also use the general Indo-European word (represented by English mere (n.)), but have no firm distinction between "sea" and "lake," either by size 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, and exist in opposite senses (e.g. Gothic saiws "lake," marei "sea;" but Dutch zee "sea," meer "lake"). Cf. also Old Norse sær "sea," but Danish sø, usually "lake" but "sea" in phrases. German See is "sea" (fem.) or "lake" (masc.). Meaning "dark area of the moon's surface" is attested from 1660s (see mare (n.2)).
Phrase sea change "transformation" is attested from 1610, first in Shakespeare ("The Tempest," I.ii). Sea anemone is from 1742; sea breeze from 1690s; sea legs is from 1712; sea level from 1806; sea serpent attested from 1640s; 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."