Denied falsely or truly (6)
I believe the answer is:
indeed
'truly' is the definition.
(synonyms)
'denied falsely' is the wordplay.
'falsely' indicates anagramming the letters.
'denied' with letters rearranged gives 'INDEED'.
'or' is the link.
(Other definitions for indeed that I've seen before include "In truth, in fact" , "To be sure" , "Certainty" , "Really; certainly" , "Word expressing surprise, disbelief, etc" .)