Lost fish of film (4)
I believe the answer is:
nemo
'lost fish of film' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for nemo that I've seen before include "Finding -, animated film" , "Jules Verne captain" , "Captain of the Nautilus" , "- me impune lacessit (motto of Scotland)" , "Jules Verne's submarine captain" .)