Complete review of ancient language, say, after study (10)
I believe the answer is:
congenital
'complete' is the definition.
(eg a 'congenital idiot', a complete fool)
'review of ancient language say after study' is the wordplay.
'review of' is a reversal indicator.
'ancient language' becomes 'Latin' (Latin is an ancient language).
'say' becomes 'eg' (short for 'exempli gratia', 'for example' in Latin).
'after' says to put letters next to each other.
'study' becomes 'con' (con can informally mean to study).
'latin'+'eg'='latineg'
'latineg' reversed gives 'genital'.
'genital' after 'con' is 'CONGENITAL'.
(Another definition for congenital that I've seen is " Absolute".)