A giant in excited eagerness (4)
I believe the answer is:
agog
'in excited eagerness' is the definition.
(I've seen this before)
'a giant' is the wordplay.
'giant' becomes 'gog' (I've seen this before).
'a'+'gog'='AGOG'
(Other definitions for agog that I've seen before include "Enthralled" , "Expecting" , "In excited eagerness" , "Unable to wait" , "All ears" .)