Genuine-sounding part of film (4)
I believe the answer is:
reel
'part of film' is the definition.
(as in a reel of film)
'genuine-sounding' is the wordplay.
'genuine' becomes 'real' (similar in meaning).
'sounding' indicates a 'sounds like' (homophone) clue.
'real' is a homophone of 'REEL'.
(Other definitions for reel that I've seen before include "Dance - sway - cotton holder" , "Part of film; dance" , "energetic dance" , "Dance - bobbin - stagger" , "Stagger about in lively dance" .)