Very eager (4)
(Other definitions for avid that I've seen before include "Keen, enthusiastic" , "Zealous, enthusiastic" , "Excessively keen" , "Fanatical" , "Showing active interest and enthusiasm" .)
'very eager' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for agog that I've seen before include "Eager, avid" , "Enthralled" , "Full of excitement" , "Very far from indifferent" , "In state of wide-eyed expectancy" .)