National kings, say, in finery that's oddly cut back (6)
I believe the answer is:
yemeni
'national' is the definition.
(I know that Yemeni is a type of national)
'kings say in finery that's oddly cut back' is the wordplay.
'kings say' becomes 'men' (king is a kind of man).
'in' means one lot of letters goes inside another.
'that's oddly cut' means one should take alternating letters (letters in odd-numbered positions removed).
'back' shows that the letters should be reversed in order.
The alternating letters of 'finery' are 'iey'.
'iey' written backwards gives 'yei'.
'men' going inside 'yei' is 'YEMENI'.
(Other definitions for yemeni that I've seen before include "from the Middle East" , "Relating to a republic on the Arabian Peninsula" , "Native of a country on the Arabian Peninsula" , "Native of, eg, Aden" , "Arab national" .)