Pledge; invective (4)
I believe the answer is:
oath
I believe this clue is a double definition.
'pledge' is the first definition.
(I've seen this before)
'invective' is the second definition.
(I've seen this in another clue)
(Other definitions for oath that I've seen before include "gadzooks!" , "Vow, sworn word" , "Curse or solemn word" , "Solemn promise to tell the truth or be loyal" , "in court, we take it" .)