Announce cut in tense film (7)
I believe the answer is:
trumpet
'announce' is the definition.
(both can mean to proclaim)
'cut in tense film' is the wordplay.
'cut' becomes 'rump' (rump is a kind of cut).
'in' indicates putting letters inside.
'tense' becomes 't' (abbreviation used in many dictionaries).
'film' becomes 'ET' (E.T. the Extra-Terrestrial).
't'+'et'='tet'
'rump' going inside 'tet' is 'TRUMPET'.
(Other definitions for trumpet that I've seen before include "Brass musical instrument" , "Loudly sound - instrument" , "Loud cry" , "Daffodil corona" , "Army instrument for signals" .)