Greek form of trance (6)
I believe the answer is:
cretan
'greek' is the definition.
(someone from the Greek island of Crete)
'form of trance' is the wordplay.
'form of' indicates anagramming the letters (the letters need to be in another 'form').
'trance' with letters rearranged gives 'CRETAN'.
(Other definitions for cretan that I've seen before include "Native of a large Greek island" , "One from largest Greek isle" , "One from Greece's largest island" , "Greek islander" , "Inhabitant of a large Greek island" .)