Cello I play for dog (6)
I believe the answer is:
collie
'dog' is the definition.
(collie is a kind of dog)
'cello i play' is the wordplay.
'play' indicates anagramming the letters.
'cello'+'i'='celloi'
'celloi' anagrammed gives 'COLLIE'.
'for' is the link.
(Other definitions for collie that I've seen before include "Silky-coated sheepdog" , "Breed of sheepdog" , "See 2" , "shepherd's gofer" , "Popular kind of sheepdog" .)