Last to look back (4)
I believe the answer is:
keep
'last' is the definition.
(thesaurus)
'look back' is the wordplay.
'look' becomes 'peek' (peek is a kind of look).
'back' says the letters should be written in reverse.
'peek' backwards is 'KEEP'.
'to' is the link.
(Other definitions for keep that I've seen before include "Retain, maintain" , "Look after" , "Central tower of castle" , "Retain or care for" , "Remain" .)