Acknowledge Charlie seen in fantastic part (6)
I believe the answer is:
accept
'acknowledge' is the definition.
(thesaurus)
'charlie seen in fantastic part' is the wordplay.
'charlie' becomes 'c' (phonetic alphabet: alpha, bravo, charlie etc.).
'seen in' is an insertion indicator.
'fantastic' becomes 'ace'.
'part' becomes 'pt' (I've seen this in other clues**).
'c' inserted inside 'ace' is 'acce'.
'acce'+'pt'='ACCEPT'
(Other definitions for accept that I've seen before include "Receive something proffered" , "Receive something offered" , "Take up, obtain" , "Consent to receive" , "Consider or hold as true" .)