Remedy gets small expletive (5)
I believe the answer is:
curse
'expletive' is the definition.
(I know that expletive can be written as curse)
'remedy gets small' is the wordplay.
'remedy' becomes 'cure' (synonyms).
'gets' means one lot of letters goes inside another (gets can mean captures or absorbs).
'small' becomes 's' (abbreviation - e.g. clothes size).
'cure' placed around 's' is 'CURSE'.
(Other definitions for curse that I've seen before include "Utter obscenities" , "Evil spell - oath" , "Execrate" , "Imprecate" , "use bad language" .)