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]

Moby Thesaurus II by Grady Ward, 1.0:

95 Moby Thesaurus words for "alacrity":
   abruptness, acquiescence, agility, agreeability, agreeableness,
   amenability, animation, anxiety, anxiousness, appetite, ardor,
   avidity, avidness, breathless impatience, briskness,
   cheerful consent, cheerful readiness, compliance, consent,
   cooperativeness, decisiveness, dispatch, docility, eagerness, elan,
   enthusiasm, expedition, expeditiousness, favorable disposition,
   favorableness, fervor, feverishness, forwardness, furiousness,
   gameness, goodwill, gust, gusto, hastiness, heartiness,
   hurriedness, immediacy, immediateness, impatience, impetuosity,
   impetuousness, impulsiveness, instantaneousness, keen desire,
   keenness, life, liveliness, nimbleness, pliability, pliancy,
   precipitance, precipitancy, precipitation, precipitousness,
   promptitude, promptness, punctuality, punctualness, quickness,
   rapidity, rashness, readiness, receptive mood, receptiveness,
   receptivity, responsiveness, right mood, sharpness, smartness,
   speed, speediness, spirit, spryness, suddenness, summariness,
   swiftness, tractability, ungrudgingness, unloathness, unreluctance,
   verve, vitality, vivacity, willing ear, willing heart, willingness,
   zeal, zealousness, zest, zestfulness