The Collaborative International Dictionary of English v.0.48:

Avidity \A*vid"i*ty\, n. [L. aviditas, fr. avidus: cf. F.
   avidit['e]. See Avid.]
   Greediness; strong appetite; eagerness; intenseness of
   desire; as, to eat with avidity.
   [1913 Webster]

         His books were received and read with avidity.
                                                  --Milward.
   [1913 Webster]

WordNet (r) 3.0 (2006):

avidity
    n 1: a positive feeling of wanting to push ahead with something
         [syn: eagerness, avidity, avidness, keenness]

Moby Thesaurus II by Grady Ward, 1.0:

57 Moby Thesaurus words for "avidity":
   acquisitiveness, alacrity, animation, anxiety, anxiousness,
   appetite, avarice, avariciousness, avidness, breathless impatience,
   cheerful readiness, covetousness, cupidity, eagerness, elan,
   forwardness, frenzy of desire, fury of desire, gluttony, grasping,
   graspingness, greed, greediness, gust, gusto, hoggishness,
   impatience, incontinence, inordinate desire, insatiability,
   insatiable desire, intemperateness, itching palm, keen desire,
   keenness, life, liveliness, lust, overgreediness, piggishness,
   promptness, quickness, rapaciousness, rapacity, ravenousness,
   readiness, sordidness, spirit, swinishness, verve, vitality,
   vivacity, voraciousness, voracity, wolfishness, zest,
   zestfulness