Have a look back (4)
I believe the answer is:
keep
'have' is the definition.
(keeping is a kind of having)
'a look back' is the wordplay.
'a look' becomes 'peek' (peek is a kind of look).
'back' is a reversal indicator.
'peek' backwards is 'KEEP'.
(Other definitions for keep that I've seen before include "Retain; part of castle" , "Retain; stronghold" , "Dungeon" , "Retain or care for" , "honour" .)