lark (n.1) Look up lark at Dictionary.com
"songbird," early 14c., earlier lauerche (c.1200), from Old English lawerce (late Old English laferce), from Proto-Germanic *laiw(a)rikon (cognates: Old Saxon lewerka, Frisian liurk, Old Norse lævirik, Dutch leeuwerik, German Lerche), of unknown origin. Some Old English and Old Norse forms suggest a compound meaning "treason-worker," but there is no folk tale to explain or support this.
lark (n.2) Look up lark at Dictionary.com
"spree, frolic," 1811, possibly shortening of skylark (1809), sailors' slang "play rough in the rigging of a ship" (larks were proverbial for high-flying), or from English dialectal lake/laik "to play" (c.1300, from Old Norse leika "to play," from PIE *leig- "to leap") with intrusive -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.