The Collaborative International Dictionary of English v.0.48:

Agog \A*gog"\, a. & adv. [Cf. F. gogue fun, perhaps of Celtic
   origin.]
   In eager desire; eager; astir.
   [1913 Webster]

         All agog to dash through thick and thin. --Cowper.
   [1913 Webster]

WordNet (r) 3.0 (2006):

agog
    adj 1: highly excited