Rambling ranter possibly (6)
I believe the answer is:
errant
'rambling' is the definition.
(thesaurus)
'ranter possibly' is the wordplay.
'possibly' is an anagram indicator.
'ranter' is an anagram of 'ERRANT'.
(Other definitions for errant that I've seen before include "Root vegetable" , "Roving" , "looking for adventure" , "so some knights are called" , "Sinful" .)