Stimulate with hot film (4)
I believe the answer is:
whet
'stimulate' is the definition.
(I know that whet is a kind of stimulate)
'with hot film' is the wordplay.
'with' becomes 'w' (short for with).
'hot' becomes 'h' (abbreviation, eg on taps).
'film' becomes 'et' (E.T. the Extra-Terrestrial).
'w'+'h'+'et'='WHET'
(Other definitions for whet that I've seen before include "grind" , "Sharpen, appetite or razor" , "appetizer" , "Edge" , "Stimulate (appetite)" .)