High-class fur fit for purpose (6)
I believe the answer is:
usable
'fit for purpose' is the definition.
(I've seen this before)
'high-class fur' is the wordplay.
'high class' becomes 'u'.
'fur' becomes 'sable' (sable is a kind of fur).
'u'+'sable'='USABLE'
(Other definitions for usable that I've seen before include "fit to wear" , "Functional and available" , "Practical" , "Of potential utility" , "at one's disposal" .)