A musician, but very good at weaving satin (7)
I believe the answer is:
pianist
'a musician' is the definition.
(pianist is a kind of musician)
'very good at weaving satin' is the wordplay.
'very good' becomes 'pi' (old-fashioned term for 'pious').
'at' says to put letters next to each other.
'weaving' indicates an anagram (letters weaved together differently).
'satin' with letters rearranged gives 'anist'.
'pi'+'anist'='PIANIST'
'but' acts as a link.
(Other definitions for pianist that I've seen before include "Musician" , "Keyboard player" , "key man" , "Key worker," , "Ivories tinkler" .)