Certain prisoner joined man and daughter (9)
I believe the answer is:
convinced
'certain' is the definition.
(similar in meaning)
'prisoner joined man and daughter' is the wordplay.
'prisoner' becomes 'con' (abbreviation for 'convict').
'joined' is a charade indicator (letters next to each other).
'man' becomes 'vince' ().
'and' says to put letters next to each other.
'daughter' becomes 'd' (genealogical abbreviation).
'con'+'vince'+'d'='CONVINCED'
(Other definitions for convinced that I've seen before include "Firmly persuaded" , "Totally certain about something" , "Absolutely certain" , "Quite sure" .)