Clue: Refinement in one of classy speech, on the surface about fifty (6)
Answer: POLISH
Explanation: Definition: Refinement
="Refinement". I think this is I="one", with POSH=*"of classy speech" *~~"classy [speech]"~~ around it ("on the surface" – similar to 'covering' etc), and all around L="fifty" in Roman numerals. *Edit thanks to ulaca.