Reminder of past dereliction (5)
I believe the answer is:
relic
'reminder' is the definition.
(thesaurus)
'of past dereliction?' is the wordplay.
'of' indicates a hidden word.
'RELIC' is hidden in the letters of 'past dereliction'.
(Other definitions for relic that I've seen before include "Ancient artefact" , "Bit of a saint, perhaps" , "Venerated memento" , "Object of historic interest" , "Item surviving from the past" .)