Ancient Edmund, behold, making a comeback (5)
I believe the answer is:
olden
'ancient' is the definition.
(thesaurus)
'edmund behold making a comeback' is the wordplay.
'edmund' becomes 'ned' (I've seen this in other clues).
'behold' becomes 'lo'.
'making a comeback' is a reversal indicator.
'ned'+'lo'='nedlo'
'nedlo' reversed gives 'OLDEN'.
(Other definitions for olden that I've seen before include "Former, past" , "Of past (times)" , "of ancient history?" , "Out of date" , "Bygone" .)