Turning up with others is most refined (6)
I believe the answer is:
purest
'most refined' is the definition.
('pure' can be similar in meaning to 'refined')
'turning up with others' is the wordplay.
'turning' says the letters should be written backwards.
'with' means one lot of letters go next to another.
'others' becomes 'rest' (eg the rest of a group).
'up' written backwards gives 'pu'.
'pu'+'rest'='PUREST'
'is' is the link.
(Other definitions for purest that I've seen before include "Most chaste or unadulterated" , "Least sullied, most virginal" , "Freest from adulteration" .)