We must get back for the cowboy film (7)
I believe the answer is:
western
'the cowboy film' is the definition.
(I've seen this before)
'we must get back' is the wordplay.
'must get' means one lot of letters go next to another.
'back' becomes 'stern' (stern means the back of a boat).
'we'+'stern'='WESTERN'
'for' acts as a link.
(Other definitions for western that I've seen before include "The Occident" , "Old film genre, horse opera" , "Type of film or music" , "Spaghetti film?" , "Cowboys and Indians movie" .)