Look up and study antique (5)
I believe the answer is:
olden
'antique' is the definition.
(thesaurus)
'look up and study' is the wordplay.
'look' becomes 'lo'.
'up' shows that the letters should be reversed in order (in down clue: letters go upwards).
'and' means one lot of letters go next to another.
'study' becomes 'den' (I've seen this before).
'lo' backwards is 'ol'.
'ol'+'den'='OLDEN'
(Other definitions for olden that I've seen before include "(Of days) in the long distant past!" , "Out of date" , "times gone by" , "as in time gone by" , "Bygone" .)