Denied falsely or truly (6)
I believe the answer is:
'truly' is the definition.
'denied falsely' is the wordplay.
'falsely' indicates an anagram.
'denied' with letters rearranged gives 'INDEED'.
'or' acts as a 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" .)