Look back and study past (5)
I believe the answer is:
olden
'past' is the definition.
(similar in meaning)
'look back and study' is the wordplay.
'look' becomes 'lo' (archaic exclamation meaning 'look!').
'back' says the letters should be written backwards.
'and' means one lot of letters go next to another.
'study' becomes 'den' (den can mean an office or study).
'lo' in reverse letter order is 'ol'.
'ol'+'den'='OLDEN'
(Other definitions for olden that I've seen before include "as in time gone by" , "Of past (times)" , "Out of date" , "Bygone" , "of ancient history?" .)