Mention freer arrangement (5)
I believe the answer is:
refer
'mention' is the definition.
(thesaurus)
'freer arrangement' is the wordplay.
'arrangement' indicates anagramming the letters.
'freer' anagrammed gives 'REFER'.
(Other definitions for refer that I've seen before include "Fail (an exam candidate)" , "Advert, mention" , "Be relevant (to)" , "Pertain; assign" , "If special treatment needed, GP might do this" .)