skylark (n.)

mid-13c. (c. 1200 as a surname), skie, sci, skei, "a cloud," from Old Norse sky "cloud," from Proto-Germanic *skeujam "cloud, cloud cover" (source also of Old English sceo (Middle English sceu) "the sky, the heavens," Old Saxon scio "cloud, region of the clouds, sky;" Old High German scuwo, Old English scua, Old Norse skuggi "shadow;" Gothic skuggwa "mirror"), from PIE root *(s)keu- "to cover, conceal."

The meaning "upper regions of the air; region of clouds, wind, and rain; the heavens, the firmament" is attested from c. 1300; it replaced native heofon in this sense (see heaven). In Middle English, the word can still mean both "cloud" and "heaven," as still in the skies (c. 1300), originally "the clouds."

Sky-high "as high as the sky" is from 1812; optimistic phrase the sky's the limit is attested from 1908. Sky-writing is from 1922. Sky-diving "sport or activity of jumping from an aircraft and free-falling before landing by parachute" is attested from 1959 (sky-diver by 1961; sky-dive (v.) by 1965).

songbird of the Old World, early 14c., earlier lauerche (c. 1200), from Old English lawerce (late Old English laferce), from Proto-Germanic *laiw(a)rikon (source also of Old Saxon lewerka, Frisian liurk, Old Norse lævirik, Dutch leeuwerik, German Lerche), a word of unknown origin.

Old English and Old Norse forms suggest a contracted compound, perhaps meaning "treason-worker," but "nothing is known in folklore to account for such a designation" [OED]. Noted for its early song and high flying (in contrast to its low nest). When the sky falls, we shall catch larks was an old proverb mocking foolish optimism.

Latin alauda "the lark" (source of Italian aloda, Spanish alondra, Provençal alauza, Old French aloe) is said to be from Gaulish (Celtic). True Latin names for the skylark were galerita, corydalus.

SPLIT the lark and you’ll find the music,

   Bulb after bulb, in silver rolled

[Emily Dickinson] 

"spree, frolic, merry adventure," 1811, slang, of uncertain origin. Possibly a shortening of skylark (1809), sailors' slang for "play rough in the rigging of a ship" (larks were proverbial for high-flying). Or perhaps it is an alteration of English dialectal or colloquial lake/laik "to play, frolic, make sport" (c. 1300, from Old Norse leika "to play," from PIE *leig- (3) "to leap") with unetymological -r- common in southern British dialect. The verb lake, considered characteristic of Northern English vocabulary, is the opposite of work but lacks the other meanings of play. As a verb, from 1813. Related: Larked; larking.