Take in sci-fi film about aliens primarily (3)
I believe the answer is:
eat
'take in' is the definition.
(synonyms)
'sci-fi film about aliens primarily' is the wordplay.
'sci-fi film' becomes 'et' (I've seen this in other clues).
'about' means one lot of letters goes inside another.
'primarily' says to take the initial letters.
The first letter of 'aliens' is 'a'.
'et' enclosing 'a' is 'EAT'.
(Other definitions for eat that I've seen before include "Munch" , "Be corrosive" , "put away" , "Scoff" , "Corrode" .)