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]