Observe one of estranged couple in film rolling over (6)
I believe the answer is:
remark
'observe' is the definition.
(synonyms)
'one of estranged couple in film rolling over' is the wordplay.
'one of estranged couple in film' becomes 'kramer' (reference to the film Kramer vs Kramer).
'rolling over' shows that the letters should be reversed in order.
'kramer' written backwards gives 'REMARK'.
(Other definitions for remark that I've seen before include "Comment or mention" , "Written or spoken comment" , "Comment, observation" , "Say as a comment" , "Make mention of" .)