With help from The Little Oxford Dictionary, 1941

sky

noun
1. the vault of heaven
2. the firmament

lark

noun
1. species of small bird, including the skylark
2. frolic, spree; an amusing incident

skylark

noun
1. Alauda arvensis, a small species of bird—plain in colouring, and not at all like its verbly cousin. The male has broad wings and two or three minutes of song in him; females prefer the male that can sing and hover the longest.

intransitive verb
1. (of sailing) to run up and down the rigging of a ship in sport
2. to gambol; to frolic; to indulge in horseplay; to indulge in lark
3. to play tricks or practical jokes

“Skylarking presents a hazard in the workplace.”
—Australian Occupational Health and Safety Legislation, 1998