Days of old (4)
I believe the answer is:
yore
'days of old' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for yore that I've seen before include "Formerly, of long ago" , "Old usage for formerly, as in days of. . ." , "Bygone time" , "Long ago (poetic)" , "Long ago (literary)" .)