Shine up the nationality (6)
I believe the answer is:
polish
'shine up the nationality' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for polish that I've seen before include "Rub until shiny" , "Refine, language" , "Rub to make the surface shine" , "Buff up - foreign language" , "Shine up in Warsaw" .)