Allow some expletives (3)
I believe the answer is:
let
'allow' is the definition.
(synonyms)
'some expletives' is the wordplay.
'some' says the answer is hidden in the clue (some of the parts of the word are used).
'LET' is hidden in the letters of 'expletives'.
(Other definitions for let that I've seen before include "Allow; tennis fault" , "Permit or rent" , "Allow or lease" , "Allowed or rented out" , "Rent out: grant" .)