Superior fur is always worth having (6)
I believe the answer is:
usable
'always worth having' is the definition.
I can't tell whether this definition defines the answer.
'superior fur' is the wordplay.
'superior' becomes 'U' (U can mean upper-class, as in U and non-U speech).
'fur' becomes 'sable' (sable is a kind of fur).
'u'+'sable'='USABLE'
'is' acts as a link.
Can you help me to learn more?
(Other definitions for usable that I've seen before include "at one's disposal" , "Functional and available" , "(Of, eg, tool) employable" , "Of potential utility" , "Serviceable" .)