Hone European language (6)
I believe the answer is:
polish
This clue is a double definition.
'hone' is the first definition.
(polishing is a kind of honing)
'european language' is the second definition.
(I've seen this before)
(Other definitions for polish that I've seen before include "elegance" , "Refine, language" , "taught in finishing school?" , "Gloss - refinement" , "Shine up in Warsaw" .)