Found in market, ELO's box set up on the shelf (8)
I believe the answer is:
obsolete
'on the shelf' is the definition.
(thesaurus)
'found in market elo's box set up' is the wordplay.
'found in' indicates a hidden word.
'set up' shows that the letters should be reversed in order (in a down clue, letters go up).
'etelosbo' can be found hidden inside 'market elos box'.
'etelosbo' back-to-front is 'OBSOLETE'.
(Other definitions for obsolete that I've seen before include "Antiquated" , "Dead" , "being out of practice" , "Outmoded, passe" , "Out-of-date" .)