Absolutely denied involvement (6)
I believe the answer is:
indeed
'absolutely' is the definition.
(both can be used to agree with something)
'denied involvement' is the wordplay.
'involvement' indicates an anagram.
'denied' with letters rearranged gives 'INDEED'.
(Other definitions for indeed that I've seen before include "Really, actually" , "Really, without doubt" , "Really - truly" , "Word expressing surprise, disbelief, etc" , "Unquestionably" .)