Enchantress keeps sum for conversion with pirate bound (12)
I believe the answer is:
circumscribe
'bound' is the definition.
(thesaurus)
'enchantress keeps sum for conversion with pirate' is the wordplay.
'enchantress' becomes 'circe' (figure of Greek myth).
'keeps' indicates putting letters inside (inserted letters are kept inside).
'for conversion' is an anagram indicator (I've seen this in other clues).
'with' says to put letters next to each other.
'pirate' becomes 'crib' (crib can mean to copy from another source).
'sum' anagrammed gives 'ums'.
'ums'+'crib'='umscrib'
'circe' enclosing 'umscrib' is 'CIRCUMSCRIBE'.
(Other definitions for circumscribe that I've seen before include "Restrict; draw round" , "put in enclosed space" , "Confine within limited range" , "Restrict, limit" .)