The Collaborative International Dictionary of English v.0.48:

Athirst \A*thirst"\, a. [OE. ofthurst, AS. ofpyrsted, p. p. of
   ofpyrstan; pref. of-, intensive + pyrstan to thirst. See
   Thirst.]
   1. Wanting drink; thirsty.
      [1913 Webster]

   2. Having a keen appetite or desire; eager; longing. "Athirst
      for battle." --Cowper.
      [1913 Webster]

WordNet (r) 3.0 (2006):

athirst
    adj 1: (usually followed by `for') extremely desirous; "athirst
           for knowledge"; "hungry for recognition"; "thirsty for
           informaton" [syn: athirst(p), hungry(p),
           thirsty(p)]