The Collaborative International Dictionary of English v.0.48:

Alacrity \A*lac"ri*ty\, n. [L. alacritas, fr. alacer lively,
   eager, prob. akin to Gr. ? to drive, Goth. aljan zeal.]
   A cheerful readiness, willingness, or promptitude; joyous
   activity; briskness; sprightliness; as, the soldiers advanced
   with alacrity to meet the enemy.
   [1913 Webster]

         I have not that alacrity of spirit,
         Nor cheer of mind that I was wont to have. --Shak.
   [1913 Webster]

WordNet (r) 3.0 (2006):

alacrity
    n 1: liveliness and eagerness; "he accepted with alacrity"; "the
         smartness of the pace soon exhausted him" [syn: alacrity,
         briskness, smartness]