The Collaborative International Dictionary of English v.0.48:

Skylark \Sky"lark`\, n. (Zool.)
   A lark that mounts and sings as it files, especially the
   common species (Alauda arvensis) found in Europe and in
   some parts of Asia, and celebrated for its melodious song; --
   called also sky laverock. See under Lark.
   [1913 Webster]

   Note: The Australian skylark (Cincloramphus cantillans) is
         a pipit which has the habit of ascending
         perpendicularly like a skylark, but it lacks the song
         of a true lark. The Missouri skylark is a pipit
         (Anthus Spraguei) of the Western United States,
         resembling the skylark in habit and song.
         [1913 Webster]

WordNet (r) 3.0 (2006):

skylark
    n 1: brown-speckled European lark noted for singing while
         hovering at a great height [syn: skylark, Alauda
         arvensis]
    v 1: play boisterously; "The children frolicked in the garden";
         "the gamboling lambs in the meadows"; "The toddlers romped
         in the playroom" [syn: frolic, lark, rollick,
         skylark, disport, sport, cavort, gambol, frisk,
         romp, run around, lark about]

Moby Thesaurus II by Grady Ward, 1.0:

21 Moby Thesaurus words for "skylark":
   carouse, celebrate, cut loose, debauch, hell around, jollify,
   jolly, lark, let go, let loose, let off steam, make merry,
   make whoopee, raise hell, revel, roister, see life, spree,
   step out, wanton, whoop it up