Assessor breaks a rule after five (6)
I believe the answer is:
valuer
'assessor' is the definition.
(thesaurus)
'breaks a rule after five' is the wordplay.
'breaks' indicates anagramming the letters.
'after' says to put letters next to each other.
'five' becomes 'v' (roman numeral).
'a'+'rule'='arule'
'arule' with letters rearranged gives 'aluer'.
'aluer' put after 'v' is 'VALUER'.
(Other definitions for valuer that I've seen before include "Assessor of the worth of things" , "A professional assessor of commercial worth" .)