Film legal professional losing weight (5)
I believe the answer is:
layer
'film' is the definition.
(film can mean a thin layer of something)
'legal professional losing weight' is the wordplay.
'legal professional' becomes 'lawyer' (I've seen this before).
'losing' indicates named letters should be taken away.
'weight' becomes 'w' (short for weight).
'lawyer' with 'w' taken out is 'LAYER'.
(Other definitions for layer that I've seen before include "One supplying eggs" , "course" , "Stratum; eg, hen" , "Source of eggs" , "Coating" .)