Look back and observe (4)
I believe the answer is:
keep
'observe' is the definition.
('keep' can be a synonym of 'observe')
'look back' is the wordplay.
'look' becomes 'peek' (peek is a kind of look).
'back' says the letters should be written backwards.
'peek' back-to-front is 'KEEP'.
'and' is the link.
(Other definitions for keep that I've seen before include "Living" , "strong position" , "Act as custodian of" , "Look after" , "Retain in old castle (4)" .)