Skylark

Skylark \SKAHY-lahrk\ , verb;
1. To frolic; sport
noun;
1. A brown-speckled European lark, Alauda arvensis, famed for its melodious song

A skylark (source)

The original meaning of this word was the bird name, which is first attested in 1686 from sky + lark. Sky dates to the early 13th century as "a cloud" from Old Norse sky ("cloud"). The Old Norse word derives from Proto-Germanic *skeujam ("cloud, cloud cover") from Proto-Indo-European *(s)keu- ("to cover, conceal"). Lark as a noun dates to the early 14th century as "songbird" from an earlier version, lauerche, which comes from Old English lawerce. Lawerce derives from Proto-Germanic *laiw(a)rikon, which is of unknown origin. The verb lark isn't attested until 1811 and is most likely a back-formation from skylark rather than an extension of the noun.

Later skylark became nautical slang for "wanton play about the rigging and tops," which lead to the verb definition by at least 1809.

Today's word and the first definition were both taken from Dictionary.com's 'Word of the Day' for Sunday, July 10
Etymologies come from the Oxford English Dictionary and/or Etymonline.com