Jack, king gets new ace, five and three finally (5)
I believe the answer is:
knave
'jack' is the definition.
(synonyms)
'king gets new ace five and three finally' is the wordplay.
I cannot really see how this works, but
'king' could be 'k' (abbreviation for king in chess) and 'k' is found in the answer.
'new' could be 'n' (common abbreviation eg NT for New Testament) and 'n' is present in the answer.
'ace' could be 'a' and 'a' is found in the answer.
'five' could be 'v' (roman numeral) and 'v' is present in the answer.
A single letter 'e' remains which might be clued in a way I don't understand.
This explanation may well be incorrect...
(Other definitions for knave that I've seen before include "Villain - card" , "Dishonest man; jack" , "pack member?" , "Jack - rogue" , "Rapscallion" .)