Offensive language recurs excessively? Not completely! (5)
I believe the answer is:
curse
'offensive language' is the definition.
'recurs excessively? not completely' is the wordplay.
'not completely' says the answer is hidden in the clue.
'CURSE' is hidden within 'recurs excessively'.
(Other definitions for curse that I've seen before include "Trouble" , "Execration" , "use bad language" , "Evil spell - oath" , "Blaspheme; damn" .)