Tend to look back (4)
I believe the answer is:
'tend' is the definition.
'look back' is the wordplay.
'look' becomes 'peek' (peek is a kind of look).
'back' says the letters should be written backwards.
'peek' written backwards gives 'KEEP'.
'to' acts as a link.
(Other definitions for keep that I've seen before include "Observe - reserve - preserve" , "run" , "Save" , "Main tower within the walls of a castle" , "Eg, beef" .)