Branch not on film (8)
I believe the answer is:
offshoot
'branch' is the definition.
(synonyms)
'not on film' is the wordplay.
'not on' becomes 'off' ('off' is the opposite to 'on').
'film' becomes 'shoot' (synonyms).
'off'+'shoot'='OFFSHOOT'
(Other definitions for offshoot that I've seen before include "Sucker" , "new branch" , "Outgrowth or by-product" , "Derivative; scion" , "Side growth" .)