In truth, the account is the truth! (8)
I believe the answer is:
veracity
'the truth' is the definition.
(thesaurus)
'in truth the account' is the wordplay.
'in' is an insertion indicator.
'truth' becomes 'verity' ('verity' can be a synonym of 'truth').
'the account' becomes 'ac'.
'verity' going around 'ac' is 'VERACITY'.
'is' acts as a link.
(Other definitions for veracity that I've seen before include "Truthfulness, accuracy" , "Habitual truthfulness" , "Exactitude" , "Truth" .)