The most common and most likely answer to this crossword clue is the 7 letter word COATING
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The straight part
We know that "film" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case film = coating.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does COATING mean?
COATING verb- To cover with a coating of some material.
- To cover like a coat.
- To clothe.
- A thin outer layer.
- Cloth for making coats.
- A telling-off; a reprimand.