An orderly part of Northern Ireland (6)
I believe the answer is:
antrim
'part of northern ireland' is the definition.
(I know that Antrim is part of Northern Ireland)
'an orderly' is the wordplay.
'orderly' becomes 'trim' (synonyms).
'an'+'trim'='ANTRIM'
(Other definitions for antrim that I've seen before include "County of Northern Ireland" , "Irish county of musically green glens" , "NI town" , "N Ireland county of green glens" , "Ulster county" .)